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;

theorem Th28:
  -R_EAL f = R_EAL((-1)(#)f) & -R_EAL f = R_EAL -f
proof
  -R_EAL f = (-1)(#)R_EAL f by MESFUNC2:9;
  hence thesis by Th20;
end;
