It is shown that the phase-space Schwinger equations can only be appropriately formulated in terms of a specific discrete procedure. Nevertheless, the solutions to Schwinger equations turn out to be independent of the discrete procedure. We stress the point that a multiplicity of representations for the quantum-mechanical amplitudes is not a peculiar eA'ect of the time-slicing definition of the path integral, but rather a necessity of the functional approach.
Physical Review. D, Particles and fields. Woodbury. Vol. 22, n. 6 (Sept. 1980), p. 1385-1389