The practice of expressing classical probability distributions on phase space in terms of underlying wavefunctions goes back at least to the 1952–1953 work of Mário Schenberg on statistical mechanics. This method was independently developed several more times, by Angelo Loinger in 1962, by Giacomo Della Riccia and Norbert Wiener in 1966, and by E. C. George Sudarshan himself in 1976.