
theorem Th59:
  for X be non empty set, S be SigmaField of X, f be PartFunc of X,ExtREAL,
  A be Element of S st f is A-measurable & A c= dom f holds
    -f is A-measurable
proof
   let X be non empty set, S be SigmaField of X, f be PartFunc of X,ExtREAL,
   A be Element of S;
   assume that
A1: f is A-measurable and
A2: A c= dom f;
   -f = (-1)(#)f by MESFUNC2:9;
   hence thesis by A1,A2,MESFUNC1:37;
end;
