Rigid Constitution is a constitution which stands above the other laws of the country, while flexible constitutions do not. A. V. Dicey defines a rigid constitution as one under which certain laws, called constitutional laws or fundamental laws "cannot be changed in the same manner as ordinary laws." A rigid constitution set forth "specific legal/constitutional obstacles to be overcome" before it may be amended, such as special approval of the people by referendum, a supermajority or special majority in the legislature, or both. In contrast, a flexible constitution is one in which the legislature may amended the constitution's content and principles through use of the ordinary legislative process. For example, the Constitution of Nigeria is rigid, while the British Constitution and the Israeli Constitution are flexible. Nigeria practices the federal system of government.