:: deftheorem Def2 defines 'nor' BVFUNC25:def 2 :
for p, q being boolean-valued Function
for b₃ being Function holds
( b₃ = p 'nor' q iff ( dom b₃ = (dom p) /\ (dom q) & ( for x being set st x in dom b₃ holds
b₃ . x = (p . x) 'nor' (q . x) ) ) );