let Y be non empty set ; :: thesis: for a, b being Function of Y,BOOLEAN holds a 'nor' (a '&' b) = 'not' (a '&' (a 'or' b))
let a, b be Function of Y,BOOLEAN; :: thesis: a 'nor' (a '&' b) = 'not' (a '&' (a 'or' b))
thus a 'nor' (a '&' b) = ('not' (a 'or' a)) 'or' ('not' (a 'or' b)) by Th33
.= 'not' (a '&' (a 'or' b)) by BVFUNC_1:14 ; :: thesis: verum