  A carefully written paper by A. Caticha [Phys. Rev. A57, 1572 (1998)] applies
consistency arguments to derive the quantum mechanical rules for compounding
probability amplitudes in much the same way as earlier work by the present
author [J. Math. Phys. 29, 398 (1988) and Int. J. Theor. Phys. 27, 543 (1998)].
These works are examined together to find the minimal assumptions needed to
obtain the most general results.
