Ras Jedir: feverish early days and freezing nights

Reda SadkiWriting

ZERZES, 4 April 2011 — “We stopped everything we were doing”, exclaims Mahfoud Bessah, the 39-year-old community-based programme coordinator at IFRC’s regional delegation in Tunis. On 21  February, he headed over to the eastern border immediately upon hearing the first reports of people crossing over. The Tunisian Red Crescent and UNHCR were already discussing how to respond. Together with Fadhel Goudil, a first aid doctor, Bessah arrived in Ras Jedir, fearing the worst.

What they found was staggering. Up to 15000 people were crossing the border from Lybia into Tunisia every day. Equally impresive was the response: spontaneous solidarity and generosity, with the local population organizing “khafila” (caravans) to carry food and other goods to those arriving at the border, whatever their origin. It is this spirit of solidarity and volunteerism that saved the day, Bessah believes, as the international community had just begun to understand the significance, scale and scope of what was being set in motion.

Two immediate challenges had to be faced. First, the near-freezing weather for border crossers with little or no shelter. Second, the very spontaneity that got things moving resulted in some logistical challenges. A gentle euphemism for what Bessah says was “n’importe quoi” (nonsense). Storage for donated goods was in short supply. People were everwhere, with nowhere to go, some carrying ridiculously large suitcases or anything else they managed to escape with.

Shelter had to be improvised. Bessah had to travel to Mednine to find a factory that could provide enough blankets. The first tents were 12 by 12 meters, intended for use during weddings or other festivities — not exactly SPHERE standards. But at least people gained some protection against the cold.

Once again, it was the spirit of volunteerism that got the tents up. Tunisian Red Crescent members did much of the heavy lifting, propelled by a sense of great urgency.

Unfortunately but somewhat predictably, these rollercoaster and sometimes haphazard early days — combined with the fact that no one in the region had ever had to deal with such a situation — have had lasting consequences.

In his initial recommandations, Bessah insisted on the fact that there was no life-threatening emergencies, no dead or dying among the “walkers” arriving: “We have to be calm, but act quickly” is how he summed it up.

Six weeks later, the flow of people crossing the border has slowed, and international media attention is now focused on the Lybian conflict itself. But the work continues as thousands more arrive. Most worrying is the fact that fewer and fewer are able to repatriate, adding pressure even when conditions are slowly improving. The International Organization for Migration (IOM) is running out of money to fund repatriation, and donor fatigue appears to be setting in. “Uncertainty characterizes the situation”, sums up Gérard Lautredou, Head of the Regional delegation. “Right now, we’ve got around 2500 people arriving each day, but what will happen if events provoke a sudden upsurge?” he asks.

IFRC is slated to open its own transit camp on 6 April, to relieve some of the pressure on the main camp, Shousha, and to allow for that camp to be reorganized to address some of the underlying causes for tension and difficulties. Nevertheless, uncertainty looms. For those ready and willing to return home, the uncertainty most difficult to bear is probably not knowing when they might be called to Djerba airport. And the fate of those convinced that going home is not an option due to fear of persecution will not resolved in the short term. All of this makes the daily work — now out of the limelight — of improving living conditions and organization even more important, whatever the numbers may be, today or tomorrow.

Reda Sadki

TOC Frankfurt Ignite! Presentation: Of Emergencies, E-Books, and Literacy

Reda SadkiWriting

In this session, Reda Sadki, will examine his own organisation’s non-profit publishing activities. With 750 publications given away each year in print and on the web, he has initiated an effort to rewire a traditional publishing workflow into a digital one, including the use of XML for layout automation, print-on-demand (POD) and e-books.

Reda Sadki is the Senior Officer for Design and Production of the International Federation of Red Cross and Red Crescent Societies, the world’s largest humanitarian organisation. For over 15 years, Reda Sadki has worked with U.N. organisations and international and local NGOs to improve visual communication by implementing high-impact design and cost-effective production workflows. The premise for his design work is that visual design and brand management for a cause are fundamentally different from mainstream advertising whose sole motive is profit. Reda has overseen design and production for numerous high-profile global reports on public health issues, including seven successive editions of the World Health Report (2001-2008). In addition, he has helped organisations improve how they organise publishing activities through careful planning and cost management of all aspects of production.

What is a system: Donella H. Meadows

What is a system?

Reda SadkiTheory

Donella H. Meadows wrote the following simple, eloquent description of what is a system:

“A system isn’t just any old collection of things.

A system must consist of three kinds of things: elements, interconnections, and a function or purpose.

A system is an interconnected set of elements that is coherently organized in a way that achieves something.

The behavior of a system cannot be known just by knowing the elements of which the system is made.

A system is more than the sum of its parts.

It may exhibit adaptive, dynamic, goal-seeking, self-preserving, and sometimes evolutionary behavior.

It is easier to learn about a system’s elements than about its interconnections.

If information-based relationships are hard to see, functions or purposes are even harder.

A system’s function or purpose is not necessarily spoken, written, or expressed explicitly, except through the operation of the system.

Purposes are deduced from behavior, not from rhetoric or stated goals.

The least obvious part of the system, its function or purpose, is often the most crucial determinant of the system’s behavior.

To ask whether elements, interconnections, or purposes are most important in a system is to ask an unsystemic question.

All are essential.

All interact.

All have their roles.

But the least obvious part of the system, its function or purpose, is often the most crucial determinant of the system’s behavior.”

Understanding what is a system is the starting point to tackling complex problems.

Meadows, Donella H., 2008.Thinking in systems: A primer. Chelsea Green Publishing.

On Air

Survivre au sida: Celebrating life to fight racism, poverty, and disease in the poor suburbs of Paris

Reda SadkiAbout me, Audio, HIV advocacy

Click on the audio player’s right arrow to listen to the radio show.

Arab and African families were hit hard by the AIDS epidemic in France. They were amongst the first to be diagnosed in the early 1980s. The conjunction of poverty and racism then resulted in thousands of infections that were preventable and deaths that – once combination therapy became available in mid-1990s – were avoidable. It is estimated that men, women, and children of Arab and African origin account for half of the 35,000 AIDS deaths during the first two decades of the epidemic in France.

Survivre au sida (Surviving AIDS) is a weekly radio programme and web site created by Reda Sadki in 1995. The show is now produced by the Comité des familles, the organization he founded in 2003 to mobilize families of all backgrounds facing HIV. But Reda stayed at the helm until 2010, when he hired a young journalist he had trained to continue his work.

Although broadcast from a small, community-access radio station in Paris, Survivre au sida in 2005 over 150,000 unique visitors each month came to the radio show’s web site. Half of them are from France and other European countries. The other half are from countries in West Africa where French is spoken. There are also listeners in Haiti and Canada.

First public demonstration by Arab and African families facing HIV in France in 2002 (Photo: Reda Sadki)
First public demonstration by Arab and African families facing HIV in France in 2002 (photo: Reda Sadki)

“Survivre au sida [Surviving AIDS] is not a radio show about AIDS. It’s about speaking to the needs of people living with HIV,” explains Reda. It’s about living with the virus, loving with the virus, and having healthy children despite the virus. “In 1995, when I started, the virus was still equated with a death sentence. Yet, a clinical trial had already demonstrated that antiretrovirals could prevent mother-to-child transmission. And the power of ‘harm reduction’ to reduce infections amongst injectors had just been recognized.”

Today, the Survivre au sida radio show celebrates the progress of medicine and its impact on the lives of families facing HIV. To love and to be loved. To have children and grand-children, knowing that (with a supportive doctor and good insurance) you will see them grow up as you grow old.

A radio report about Survivre au sida, on celebrating life with HIV while facing racism and poverty

This report by Michel Arseneault for Radio France International (RFI), first broadcast on 11 December 2006, is the only time an English-language journalist documented this singular story of how families facing HIV, poverty, and disease responded to a radio show’s call for empowerment by speaking for themselves, in their own names, and for their own needs.

George Siemens at TEDxNYED (3 June 2010)

A few of my favorite excerpts from George Siemens’s Knowing Knowledge (2006)

Reda SadkiTheory

My own practice (and no doubt yours) has been shaped by many different learning theorists. George Siemens, for me, stands out articulating what I felt but did not know how to express about the changing nature of knowledge in the Digital Age. Below I’ve compiled a few of my favorite excerpts from his book Knowing Knowledge, published in 2006, two years before he taught the first Massive Open Online Course (MOOC) with Alec Couros and Stephen Downes.

Learning has many dimensions. No one model or definition will fit every situation. CONTEXT IS CENTRAL. Learning is a peer to knowledge. To learn is to come to know. To know is to have learned. We seek knowledge so that we can make sense. Knowledge today requires a shift from cognitive processing to pattern recognition.

Figure 5 Knowledge types

Construction, while a useful metaphor, fails to align with our growing understanding that our mind is a connection-creating structure. We do not always construct (which is high cognitive load), but we do constantly connect.

We learn foundational elements through courses…but we innovate through our own learning.

Figure 17 Learning and knowledge domains

The changing nature of knowledge

The Achilles heel of existing theories rests in the pace of knowledge growth. All existing theories place processing (or interpretation) of knowledge on the individual doing the learning. This model works well if the knowledge flow is moderate. A constructivist view of learning, for example, suggests that we process, interpret, and derive personal meaning from different information formats. What happens, however, when knowledge is more of a deluge than a trickle? What happens when knowledge flows too fast for processing or interpreting?

Figure 23 Knowledge as process, not product

Knowledge has broken free from its moorings, its shackles. Those, like Francis Bacon, who equate knowledge with power, find that the masses are flooding the pools and reservoirs of the elite. […] The filters, gatekeepers, and organizers are awakening to a sea of change that leaves them adrift, clinging to their old methods of creating, controlling, and distributing knowledge. […] Left in the wake of cataclysmic change are the knowledge creation and holding structures of the past. The ideologies and philosophies of reality and knowing—battle spaces of thought and theory for the last several millennia—have fallen as guides.

Libraries, schools, businesses—engines of productivity and society—are stretching under the heavy burden of change. New epistemological and ontological theories are being formed, as we will discuss shortly with connective knowledge. These changes do not wash away previous definitions of knowledge, but instead serve as the fertile top of multiple soil layers. […]

Or consider email in its earlier days—many printed out a paper copy of emails, at least the important ones, and filed them in a file cabinet. Today we are beginning to see a shift with email products that archive and make email searchable and allow individuals to apply metadata at point of use (tagging).

Knowledge has to be accessible at the point of need. Container-views of knowledge, artificially demarcated (courses, modules) for communication, are restrictive for this type of flow and easy-access learning.

Everything is going digital. The end user is gaining control, elements are decentralizing, connections are being formed between formerly disparate resources and fields of information, and everything seems to be speeding up.

“Know where” and “know who” are more important today that knowing what and how.

Figure 16 Know Where

Once flow becomes too rapid and complex, we need a model that allows individuals to learn and function in spite of the pace and flow.

We need to separate the learner from the knowledge they hold. It is not really as absurd as it sounds. Consider the tools and processes we currently use for learning. Courses are static, textbooks are written years before actual use, classrooms are available at set times, and so on.

The underlying assumption of corporate training and higher education centers on the notion that the world has not really changed.

But it has. Employees cannot stay current by taking a course periodically. Content distribution models (books and courses) cannot keep pace with information and knowledge growth. Problems are becoming so complex that they cannot be contained in the mind of one individual—problems are held in a distributed manner across networks, with each node holding a part of the entire puzzle. Employees require the ability to rapidly form connections with other specialized nodes (people or knowledge objects). Rapidly creating connections with others results in a more holistic view of the problem or opportunity, a key requirement for decision making and action in a complex environment.

How do we separate the learner from the knowledge? By focusing not on the content they need to know (content changes constantly and requires continual updating), but on the connections to nodes which continually filter and update content.

Here is what the connectivism implementation cycle looks like as a mind map. (Click on the image to download the PDF).

Connectivism implementation cycle (George Siemens, 2006)

Source: George Siemens, Knowing Knowledge (2006).

Image: TEDxNYED

Tuberculosis in Algeria

Colonialism and disease: tuberculosis in Algeria

Reda SadkiGlobal health

Tuberculosis in Algeria as part of colonization: high death rates and false explanations

During French colonial rule in Algeria (1830-1962), tuberculosis became a major killer disease.

The French brought this deadly sickness with them when they invaded Algeria.

Before the French came, tuberculosis was not a big problem for Algerian people.

The disease spread quickly through Algerian communities during colonial times.

By the 1930s and 1940s, studies showed that tuberculosis infection rates were very high.

In 1938, about 5 out of every 100 Algerian people got infected with tuberculosis each year.

By 1948, this number was still about 4 out of every 100 people.

Around 300 out of every 100,000 Algerians got tuberculosis each year before independence.

Why tuberculosis in Algeria spread so fast under colonial rule

The French colonial system created perfect conditions for tuberculosis to spread among Algerian people.

The colonial government took away good land from Algerians and forced them to live in crowded, poor areas.

French policies of displacement, starvation, and impoverishment made Algerian society very weak.

People lived in terrible conditions without clean water, good food, or proper housing.

French colonial reports show that Algerians died from tuberculosis at much higher rates than French settlers.

Although the number of infections was small compared to the French colonists, the death rate among Algerians was high.

This happened because Algerians could not get proper medical care and lived in much worse conditions than the French people.

During periods of drought, locusts, and famine, many Algerians had to move toward cities like Algiers.

They carried diseases with them because they were weak from hunger and poor living conditions.

The French authorities put them in shelters and prisons, but this did not stop tuberculosis from spreading to French areas too.

False colonial explanations for tuberculosis in Algeria: blaming Algerian people

French colonial doctors and officials did not want to admit that their policies caused the tuberculosis disaster.

Instead, they created false explanations that blamed Algerian people themselves for getting sick.

Colonial doctors said that Algerians got tuberculosis because they were naturally inferior to French people.

They claimed that Arab and Berber people had weak bodies and minds that could not fight disease.

French medical writings described Algerians as lazy, criminal, incompetent, and prone to bad behavior.

They said these supposed character flaws made Algerians more likely to get sick.

Colonial doctors also claimed that Algerian culture and religion made people vulnerable to disease.

They criticized traditional Algerian healing practices and said that Islamic beliefs prevented people from getting proper medical care.

French medical officials argued that only Western medicine could help Algerians, but they made sure that most Algerian people could not access good medical treatment.

Some French doctors wrote that the “inferior populations” of Arabs and other non-European groups naturally weakened the health of everyone in Algeria.

They used racist theories to explain why tuberculosis spread so fast, rather than looking at the terrible living conditions that French policies had created.

The French colonial medical service was set up mainly to protect French settlers, not to help Algerian people.

Colonial doctors saw their job as keeping French people healthy and safe from local diseases, not as caring for the Algerian population that suffered the most from tuberculosis.

Independence and the fight against tuberculosis in Algeria

When Algeria became independent in 1962, the new government inherited a serious tuberculosis problem.

The disease was still killing many people across the country.

But instead of accepting this situation, Algerian leaders decided to fight tuberculosis with scientific methods and strong public health programs.

Early steps after independence

Right after independence, Algeria faced many challenges.

The country was poor, and the health system was very weak.

Few doctors remained in the country, and there were not enough hospitals or medical supplies.

Despite these problems, the new Algerian government made tuberculosis control a top priority.

In 1964, Algeria established the Tuberculosis Office (Bureau de la Tuberculose).

This office began organizing a national fight against the disease.

The government also started working with the World Health Organization to learn the best ways to treat and prevent tuberculosis.

Between 1966 and 1967, studies showed that tuberculosis infection rates were already starting to drop in Algeria.

The annual risk of getting tuberculosis fell in different regions, showing that the new approach was working.

The national tuberculosis control program

In December 1972, Algeria launched its first National Tuberculosis Control Program.

This program had clear goals: to integrate anti-tuberculosis activities into all health sectors nationwide and to create a unified, systematic approach to tuberculosis control.

The program also standardized evaluation methods so doctors could monitor and assess tuberculosis prevention and treatment efforts effectively.

Algeria also established a National Tuberculosis Control Laboratory, which became the national reference center for research on tuberculosis.

This laboratory played a key role in strengthening tuberculosis diagnosis and research, helping the country fight the disease more effectively.

Pierre Chaulet and the tuberculosis revolution

One of the most important figures in Algeria’s fight against tuberculosis was Dr. Pierre Chaulet.

Chaulet was a French doctor who had supported Algerian independence and stayed in the country after 1962 to help build the new health system.

Chaulet worked at Mustapha University Hospital in Algiers and became a leading tuberculosis researcher.

He met with international experts and learned about new treatment methods that could cure tuberculosis much faster than old treatments.

In the 1970s, Chaulet and his team tested new drug combinations that could cure tuberculosis in just six months instead of the years of treatment that had been needed before.

These shorter treatments were much easier for patients to complete, which meant more people got fully cured.

Amazing results: how did the rates of tuberculosis in Algeria drop so fast?

The results of Algeria’s tuberculosis program were remarkable.

The World Health Organization reported that tuberculosis rates in Algeria fell dramatically after independence:

  • 1975: 78 cases per 100,000 people;
  • 1981: 60 cases per 100,000 people;
  • By the 2000s: Below 26 cases per 100,000 people;
  • 2016: Below 17 cases per 100,000 people;
  • 2023: Only 9.4 cases per 100,000 people.

In 1980, Algeria adopted the six-month tuberculosis treatment as standard care across the entire country.

This treatment approach became a model that eradicated tuberculosis in Algeria and was later copied by other nations around the world.

Key factors in Algeria’s success

Several important factors helped Algeria succeed in fighting tuberculosis:

Free healthcare for all: Algeria established free healthcare that allowed access for most of the population.

This meant that poor people could get tuberculosis treatment without paying money.

BCG vaccination program: Algeria started vaccinating all newborn babies with BCG vaccine, which helps prevent tuberculosis.

Within one year, they achieved nearly 90% vaccination coverage.

This large-scale immunization effort greatly reduced tuberculosis risk, especially among children.

Better diagnosis: Algeria expanded microscopy laboratories, which improved tuberculosis diagnosis by enabling doctors to confirm the disease in 85% of new lung tuberculosis cases.

This advance meant more accurate detection and treatment of infectious cases, reducing disease transmission.

Standardized treatment: Algeria adopted a six-month treatment regimen for all forms of tuberculosis across all health sectors.

This standardized approach, following global recommendations, significantly improved treatment outcomes and patient recovery rates.

Training and education: The government trained many health workers in tuberculosis care and prevention.

This created a network of skilled staff who could identify and treat tuberculosis cases throughout the country.

The contrast: colonial failure versus independence success

The difference between tuberculosis control under French colonial rule and after Algerian independence is striking and clear.

Under colonial rule (1830-1962)

  • Tuberculosis rates were extremely high (around 300 cases per 100,000 people);
  • Algerians died from tuberculosis at much higher rates than French settlers;
  • Colonial policies created perfect conditions for disease spread through poverty, overcrowding, and malnutrition;
  • French doctors blamed Algerian people for getting sick rather than addressing the real causes;
  • Medical care was designed mainly to protect French settlers, not to help Algerian people;
  • The colonial system lasted 132 years without solving the tuberculosis problem.

After independence (1962-present)

  • Tuberculosis rates dropped dramatically in just a few decades;
  • Algeria achieved nearly complete tuberculosis eradication by international standards;
  • The government addressed root causes through free healthcare, better living conditions, and comprehensive public health programs;
  • Algerian and international doctors worked together using scientific methods;
  • Medical care was designed to serve all Algerian people equally;
  • Major progress was achieved within 20 years, with continued improvement over 60 years.

What the evidence shows

The historical evidence proves several important points:

Colonial rule made tuberculosis worse: The French colonial system created the conditions that allowed tuberculosis to spread rapidly among Algerian people.High infection rates, poor living conditions, and limited medical care for Algerians were direct results of colonial policies.

Racist explanations were false: French colonial doctors blamed Algerian culture and supposed racial inferiority for high tuberculosis rates.

This was completely wrong.

When Algerians gained control of their own healthcare system after independence, they quickly brought tuberculosis under control using the same scientific methods available to French doctors.

Independence brought real solutions: Once Algeria became independent, the government was able to address the real causes of tuberculosis: poverty, malnutrition, overcrowding, and lack of medical care.

By fixing these problems and providing free healthcare to all people, Algeria achieved what the colonial system never could.

Scientific medicine works when applied fairly: The same medical knowledge that was available during colonial times became much more effective after independence because it was applied to serve all Algerian people, not just French settlers.

Lessons for today

Algeria’s victory over tuberculosis teaches important lessons about health, colonialism, and independence:

Health problems have social and political causes: Tuberculosis spread in colonial Algeria not because of Algerian people’s character or culture, but because of unjust policies that created poverty and poor living conditions.

Racist explanations hide the real problems: When health officials blame sick people for their illness instead of addressing unfair social conditions, they prevent real solutions from being found.

Public health requires political commitment: Algeria succeeded against tuberculosis because the independent government made it a priority and committed resources to serve all people equally.

International cooperation helps when based on equality: Algeria worked successfully with international health experts after independence because these relationships were based on mutual respect rather than colonial domination.

Algeria’s experience shows that with proper political commitment, adequate resources, and scientific methods applied fairly, even the most serious health problems can be solved.

The country transformed from having one of the world’s worst tuberculosis problems to achieving near-eradication in just a few decades.

Bibliography

  1. Bentata, K., Alihalassa, S., Gharnaout, M., Bennani, M. A., & Berrabah, Y. (2025). Algerian Tuberculosis Control Program: 60 Years of Successful Experience. Cureus, 17(6), e86357. http://dx.doi.org/10.7759/cureus.86357
  2. Guedim, T., 2024. History of epidemics and preventive medicine in Algeria during the modern and contemporary period: Infectious diseases and quarantine as a model. ijhs 8, 376–386. https://doi.org/10.53730/ijhs.v8nS1.14783
  3. Chopin, C. A. (2015). Embodying ‘the new white race’: colonial doctors and settler society in Algeria, 1878-1911. Social History of Medicine, 28(4), 735-752. http://dx.doi.org/10.1093/shm/hkv066
  4. Clark, H. L. (2016). Expressing entitlement in colonial Algeria: villagers, medical doctors, and the state in the early 20th century. International Journal of Middle East Studies, 48(3), 445-472. http://dx.doi.org/10.1017/S0020743816000587
  5. Stafford, N. (2013). Pierre Chaulet. BMJ, 346, f571. http://dx.doi.org/10.1136/bmj.f571
  6. Velmet, A. (2019). The making of a Pastorian empire: tuberculosis and bacteriological technopolitics in French colonialism and international science, 1890–1940. Journal of Global History, 14(2), 279-300. http://dx.doi.org/10.1017/S0022050719000639
  7. Gallois, W., 2007. Local Responses to French Medical Imperialism in Late Nineteenth-Century Algeria. Social History of Medicine 20, 315–331. https://doi.org/10.1093/shm/hkm037
  8. Chaulet, P. (1989). Tuberculosis: a six-month Cure. World Health Forum, 10(1), 116-122.
How to solve it

How to Solve It

Reda SadkiCulture, Learning, Quotes

Understanding the problem

First. You have to understand the problem.

  • What is the unknown? What are the data? What is the condition?
  • Is it possible to satisfy the condition? Is the condition sufficient to determine the unknown? Or is it insufficient? Or redundant? Or contradictory?
  • Draw a figure. Introduce suitable notation.
  • Separate the various parts of the condition. Can you write them down?

Devising a plan

Second. Find the connection between the data and the unknown. You may be obliged to consider auxiliary problems if an immediate connection cannot be found. You should obtain eventually a plan of the solution.

  • Have you seen it before? Or have you seen the same problem in a slightly different form?
  • Do you know a related problem? Do you know a theorem that could be useful?
  • Look at the unknown! And try to think of a familiar problem having the same or a similar unknown.
  • Here is a problem related to yours and solved before. Could you use it? Could you use its result? Could you use its method? Should you introduce some auxiliary element in order to make its use possible?
  • Could you restate the problem? Could you restate it still differently? Go back to definitions.
  • If you cannot solve the proposed problem try to solve first some related problem. Could you imagine a more accessible related problem? A more general problem? A more special problem? An analogous problem? Could you solve a part of the problem? Keep only a part of the condition, drop the other part; how far is the unknown then determined, how can it vary? Could you derive something useful from the data? Could you think of other data appropriate to determine the unknown? Could you change the unknown or data, or both if necessary, so that the new unknown and the new data are nearer to each other?
  • Did you use all the data? Did you use the whole condition? Have you taken into account all essential notions involved in the problem?

Carrying out the plan

Third. Carry out your plan.

  • Carrying out your plan of the solution, check each step.
  • Can you see clearly that the step is correct?
  • Can you prove that it is correct?

Looking Back

Fourth. Examine the solution obtained.

  • Can you check the result? Can you check the argument?
  • Can you derive the solution differently? Can you see it at a glance?
  • Can you use the result, or the method, for some other problem?

Summary taken from G. Polya, “How to Solve It”, 2nd ed., Princeton University Press, 1957, ISBN 0–691–08097–6.