theorem :: CFUNCT_1:78

for X, Y being set
for C being non empty set
for f1, f2 being PartFunc of C,COMPLEX st f1 | X is constant & f2 | Y is constant holds
( (f1 + f2) | (X /\ Y) is constant & (f1 - f2) | (X /\ Y) is constant & (f1 (#) f2) | (X /\ Y) is constant )