Article 19 Freedom of opinion may not be prejudiced. Every person shall have the right to express his opinion and to circulate it orally, in writing or in any form of expression or art, with due consideration to the provisions of the law. Article 20 Freedom of residence and movement shall be guaranteed within the limits of the law. Article 21 1. The economic system in Palestine shall be based on the principles of a free market economy. The executive branch may establish public companies that shall be regulated by a law. 2. Freedom of economic activity is guaranteed. The law shall define the rules governing its supervision and their limits. 3. Private property, both real estate and movable assets, shall be protected and may not be expropriated except in the public interest and for fair compensation in accordance with the law or pursuant to a judicial ruling. 4. Confiscation shall be in accordance with a judicial ruling. Article 22 1. Social, health, disability and retirement insurance shall be regulated by law. 2. Maintaining the welfare of families of martyrs, prisoners of war, the injured and the disabled is a duty that shall be regulated by law. The National Authority shall guarantee these persons education, health and social insurance. Article 23 Every citizen shall have the right to proper housing. The Palestinian National Authority shall secure housing for those who are without shelter. Article 24 1. Every citizen shall have the right to education. It shall be compulsory until at least the end of the basic level. Education shall be free in public schools and institutions. 2. The National Authority shall supervise all levels of education and its institutions, and shall strive to upgrade the educational system. 3. The law shall guarantee the independence of universities, institutes of higher education, and scientific research centers in a manner that guarantees the freedom of scientific research as well as literary, artistic and cultural creativity. The National Authority shall encourage and support such creativity.