Let R = {a + bi|a, b ∈ Z, i2 = -1}, with addition and multiplication defined by (a + bi) + (c + di) = (a + c) + (b + d)i and (a + bi)(c + di) = (ac - bd) + (be + ad)i, respectively. (a) Verify that R is an integral domain, (b) Determine all units in R.