High Quality Content by WIKIPEDIA articles! In mathematics, the Weil conjecture on Tamagawa numbers was formulated by André Weil in the late 1950s and proved in 1989. It states that the Tamagawa number (G), where G is any connected and simply connected semisimple algebraic group G, defined over a number field K, satisfies (G) = 1. Here simply connected has the usual meaning for algebraic group theory, of not having a proper algebraic covering, which is not exactly the topologists' meaning in all cases.