reserve k,n,m,l,p for Nat;
reserve n0,m0 for non zero Nat;

theorem Th5:
  {n,m} is finite Subset of NAT
proof
  n in NAT & m in NAT by ORDINAL1:def 12;
  hence {n,m} is finite Subset of NAT by ZFMISC_1:32;
end;
