A new global operator for two-particle delta functions

A new type of global operator to be used in evaluating matrix elements of two-particle delta functions is introduced. It is based, like the Trivedi (1980) one-particle operator, on the Poisson equation and is easier to apply than the method of Hiller et al. (1978). After a test in the helium isoelectronic sequence, the new method is applied successfully to the interesting problem of hyperfine structure in muonic helium.