reserve
   a,b,c,x,y,z,A,B,C,X,Y for set,
   f,g for Function,
   V for SetValuation,
   P for Permutation of V,
   p,q,r,s for Element of HP-WFF,
   n for Element of NAT;

theorem Lm18: x<>{} implies x tohilb=id 1
proof
assume x<>{}; then
reconsider xx=x as non empty set;
xx tohilb=id 1;
hence thesis;
end;
