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;
reserve X for non empty set,
  S for SigmaField of X,
  f,g for PartFunc of X,REAL,
  A for Element of S,
  r for Real,
  p for Rational;
reserve X for non empty set,
  f,g for PartFunc of X,REAL,
  r for Real ;

theorem
  for x being set st x in dom f & max-f.x = -(f.x) holds max+f.x = 0
proof
  let x be set;
  assume that
A1: x in dom f and
A2: max-f.x = -(f.x);
  -(f.x) = max-(R_EAL f).x by A2,Th30;
  then -((R_EAL f).x) = max-(R_EAL f).x by SUPINF_2:2;
  then max+(R_EAL f).x =0. by A1,MESFUNC2:21;
  hence thesis by Th30;
end;
