let Y be set ; :: thesis: for C being non empty set
for f being PartFunc of C, COMPLEX
for q being Element of COMPLEX st f | Y is constant holds
(q (#) f) | Y is constant
let C be non empty set ; :: thesis: for f being PartFunc of C, COMPLEX
for q being Element of COMPLEX st f | Y is constant holds
(q (#) f) | Y is constant
let f be PartFunc of C, COMPLEX ; :: thesis: for q being Element of COMPLEX st f | Y is constant holds
(q (#) f) | Y is constant
let q be Element of COMPLEX ; :: thesis: ( f | Y is constant implies (q (#) f) | Y is constant )
assume f | Y is constant ; :: thesis: (q (#) f) | Y is constant
then consider r being Element of COMPLEX such that
A1: for c being Element of C st c in Y /\ (dom f) holds
f /. c = r by PARTFUN2:54;

now

let c be Element of C; :: thesis: ( c in Y /\ (dom (q (#) f)) implies (q (#) f) /. c = q * r )
assume c in Y /\ (dom (q (#) f)) ; :: thesis: (q (#) f) /. c = q * r
then A2: ( c in dom (q (#) f) & c in Y ) by XBOOLE_0:def 4;
then c in dom f by Th7;
then A3: c in Y /\ (dom f) by A2, XBOOLE_0:def 4;
thus (q (#) f) /. c = q * (f /. c) by A2, Th7
.= q * r by A1, A3 ; :: thesis: verum

end;

hence (q (#) f) | Y is constant by PARTFUN2:54; :: thesis: verum