consumer’s indifference curves

Two people trade two goods that they cannot produce. Suppose that one consumer’s indifference curves are bowed away from the origin—the usual type of curves—but the other’s are concave to the origin. In an Edgeworth box, show that a point of tangency between the two consumers’ indifference curves is not a Pareto-efficient bundle. (Hint: Identify another allocation that is Pareto superior.)