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 = 0 holds max-f.x = -(f.x)
proof
  let x be set;
  assume that
A1: x in dom f and
A2: max+f.x =0;
  0 = max+(R_EAL f).x by A2,Th30;
  then max-(R_EAL f).x =-((R_EAL f).x) by A1,MESFUNC2:20;
  then max-f.x =-((R_EAL f).x) by Th30;
  hence thesis by SUPINF_2:2;
end;
