reserve f, g, h for Function;
reserve x, y, z, u, X for set,
  A for non empty set,
  n for Element of NAT,
  f for Function of X, X;
reserve f for c=-monotone Function of bool X, bool X,
  S for Subset of X;

theorem Th6:
  f.S c= S implies lfp(X,f) c= S
proof
  set H = {h where h is Subset of X : f.h c= h };
  assume f.S c= S;
  then S in H;
  hence thesis by SETFAM_1:3;
end;
