reserve X for non empty set,
  Y for set,
  S for SigmaField of X,
  F for sequence of S,
  f,g for PartFunc of X,REAL,
  A,B for Element of S,
  r,s for Real,
  a for Real,
  n for Nat;

theorem Th12:
  f is A-measurable iff for r being Real holds A /\
  less_dom(f,r) in S by MESFUNC1:def 16;
