:: deftheorem Def7 defines 'eqv' BVFUNC_1:def 7 :
for p, q being boolean-valued Function
for b₃ being Function holds
( b₃ = p 'eqv' q iff ( dom b₃ = (dom p) /\ (dom q) & ( for x being set st x in dom b₃ holds
b₃ . x = (p . x) <=> (q . x) ) ) );