:: deftheorem defines (#) MESFUNC1:def 5 :
for C being non empty set
for f1, f2 being b₁ -defined ExtREAL -valued Function
for b₄ being PartFunc of C,ExtREAL holds
( b₄ = f1 (#) f2 iff ( dom b₄ = (dom f1) /\ (dom f2) & ( for c being Element of C st c in dom b₄ holds
b₄ . c = (f1 . c) * (f2 . c) ) ) );