:: deftheorem Def1 defines + VALUED_1:def 1 :
for f1, f2 being complex-valued Function
for b₃ being Function holds
( b₃ = f1 + f2 iff ( dom b₃ = (dom f1) /\ (dom f2) & ( for c being object st c in dom b₃ holds
b₃ . c = (f1 . c) + (f2 . c) ) ) );