,;??I2The cusp c o n d i t i o n s a r e derived which d e s c r i b e t h e behavior of t h e wave f u n c t i o n a t t h e s i n g u l a r i t l e s of t h e Coulomb p o t e n t i a l corresponding t o t h e coalescence of two or more p a r t i c l e s .
The techn -j i hies involved in some of the recut developments in low r order perturbation theory are discussed in detail. 'these include: the close two-gjay relationship between the perturbation solutions-and the
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