let M1, M2 be Function of X,REAL; ( ( for x being set st x in X holds
M1 . x = min (r,(f . x)) ) & ( for x being set st x in X holds
M2 . x = min (r,(f . x)) ) implies M1 = M2 )
assume that
A3:
for x being set st x in X holds
M1 . x = min (r,(f . x))
and
A4:
for x being set st x in X holds
M2 . x = min (r,(f . x))
; M1 = M2
hence
M1 = M2
by FUNCT_2:12; verum