
theorem
  for T being Nat holds
   {w where w is Element of NAT: w>0 & w<=T} c=
     {w where w is Element of NAT: w<=T}
proof
  let T be Nat;
  let x be object;
  assume x in {w where w is Element of NAT: w>0 & w<=T}; then
  consider w being Element of NAT such that B1: x=w & w>0 & w<=T;
  thus thesis by B1;
end;
