theorem
  <=6n+1(m) = <=6n+1(n) implies m = n
  proof
    assume
A1: <=6n+1(m) = <=6n+1(n);
    assume m <> n;
    then m < n or m > n by XXREAL_0:1;
    hence thesis by A1,Th10;
  end;
