Let (M1,δ1) and (M2,δ2) be metric spaces. Denote by M = M1 ×M2 the Carte- sian product of M1 and M2 and by (M, d1) the product space where d1 is the metric defined in Proposition 3.20. Show (briefly) that if (M1,δ1) and (M2,δ2) are compact metric spaces, then so is (M, d1).