States that do not provide for any rule concerning the form of the texts submitted to referendum logically do not adopt the principle of unity of form either. By contrast, when a single form is prescribed, this principle is imposed by definition. Certain states that provide for several types of referendum adopt the principle of unity of form. This principle is expressly laid down in Switzerland but is implicit to a greater or lesser extent in quite a number of other states (for example, in Albania a vote is held on constitutional provisions, the repeal of legislation or a question of principle). A similar situation may be said to exist in Andorra, Estonia, Greece, Hungary, Lithuania and Spain.