for X being non empty set
for S being SigmaField of X
for M being sigma_Measure of S
for A being Element of S
for c being R_eal st c <> +infty & c <> -infty holds
ex f being PartFunc of X,ExtREAL st
( f is_simple_func_in S & dom f = A & ( for x being object st x in A holds
f . x = c ) )