theorem Th44: :: RFUNCT_1:44

for X being set
for f1, f2 being complex-valued Function holds
( (f1 + f2) | X = (f1 | X) + (f2 | X) & (f1 + f2) | X = (f1 | X) + f2 & (f1 + f2) | X = f1 + (f2 | X) )