let Y be non empty set ; :: thesis: for a, b being Element of Funcs (Y,BOOLEAN) holds a 'nor' (a 'or' b) = 'not' (a 'or' b)
let a, b be Element of Funcs (Y,BOOLEAN); :: thesis: a 'nor' (a 'or' b) = 'not' (a 'or' b)
thus a 'nor' (a 'or' b) = 'not' ((a 'or' a) 'or' b) by Th34
.= 'not' (a 'or' b) ; :: thesis: verum