
theorem Th3:
  for X be non empty set, A be set, f be PartFunc of X,ExtREAL
     holds -(f|A) = (-f)|A
proof
  let X be non empty set, A be set, f be PartFunc of X,ExtREAL;
  -(f|A) = (-1)(#)(f|A) by MESFUNC2:9; then
  -(f|A) = ((-1)(#)f)|A by Th2;
  hence thesis by MESFUNC2:9;
end;
