let Y be set ; :: thesis: for C being non empty set
for f being PartFunc of C,REAL st f | Y is constant holds
(- f) | Y is constant
let C be non empty set ; :: thesis: for f being PartFunc of C,REAL st f | Y is constant holds
(- f) | Y is constant
let f be PartFunc of C,REAL; :: thesis: ( f | Y is constant implies (- f) | Y is constant )
(- f) | Y = - (f | Y) by Th46;
hence ( f | Y is constant implies (- f) | Y is constant ) ; :: thesis: verum