A.R. Meijer

The problem of the title, that of flipping a coin by telephone, was proposed and solved by Manuel Blum [19821. One cannot do better in sketching the problem than by quoting the first paragraph of his abstract:

Alice and Bob want to flip a coin by telephone. (They have just divorced, live in different cities, want to decide who gets the car.) Bob would not like to tell Alice HEADS and hear Alice (at the other end of the line) say Here goes, . . . I'm flipping the coin . . . You lost!