reserve X for non empty set,
  Y for set,
  S for SigmaField of X,
  M for sigma_Measure of S,
  f,g for PartFunc of X,COMPLEX,
  r for Real,
  c for Complex,
  E,A,B for Element of S;

theorem Th26:
  for k be Real, X,S,E for f be PartFunc of X,REAL st f is
  nonnegative & 0 <= k holds (f to_power k) is nonnegative;
