theorem Th51: :: CFUNCT_1:52

for X being set
for C being non empty set
for f1, f2 being PartFunc of C,COMPLEX holds
( (f1 + f2) | X = (f1 | X) + (f2 | X) & (f1 + f2) | X = (f1 | X) + f2 & (f1 + f2) | X = f1 + (f2 | X) )