
theorem Th30:
for X be non empty set, S be SigmaField of X, f be PartFunc of X,ExtREAL
 st f is_simple_func_in S holds -f is_simple_func_in S
proof
   let X be non empty set, S be SigmaField of X, f be PartFunc of X,ExtREAL;
   assume A1:f is_simple_func_in S;
   -f = (-1)(#)f by MESFUNC2:9;
   hence -f is_simple_func_in S by A1,MESFUNC5:39;
end;
