"For example, assume that A created a trust in 1940 providing for payment of the income to B for life with the power in B to amend the trust, and for payment of the remainder to such persons as B shall appoint or, upon default of appointment, to C. If B amended the trust in 1948 by providing that upon his death the remainder was to be paid to D, and if he further amended the trust in 1955 by deleti" . . . .