rw [Order.grlex]
n : ℕ
a b c : Variables n order.GrLex
h_le : Order.grlex a b
⊢ Order.grlex (Variables.mul a c) (Variables.mul b c)
n : ℕ
a b c : Variables n order.GrLex
h_le : Order.grlex a b
⊢ let sum₁ := Order.grlex.elem_sum (Variables.mul a c);
  let sum₂ := Order.grlex.elem_sum (Variables.mul b c);
  if sum₁ < sum₂ then True
  else if sum₁ = sum₂ then if Order.lex (Variables.mul a c) (Variables.mul b c) then True else False else False