 reserve i,j,k,k0,m,n,N for Nat;
 reserve x,y for Real;
 reserve p for Prime;

theorem NatOneLe:
  k is non zero iff 1 <= k
  proof
    hereby
      assume k is non zero;
      then 0+1 <= k by NAT_1:13;
      hence 1 <= k;
    end;
    thus thesis;
  end;
