1955 (not 1995), Greece issued a stamp with a pattern consisting of three chessboards. This stamp commemorates the Pythagorean School, a school and religious group in Greece 2,500 years ago, its establishment and its cultural contribution. The design on the stamp is an explanation of a very important theorem in mathematics. It is the most wonderful, famous and useful theorem in elementary geometry. In our country, people call it Pythagorean theorem or quotient height theorem; In Europe, people call it Pythagoras theorem.

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