Three-body problems with $\delta$-functional potentials

Possible realizations of three-particle singular Hamiltonians corresponding to $\delta$-functional two-body potentials are described. The scheme used to describe the singular potentials is essentially the same as Shirokov's [1, 2]. It is shown that besides the classical model [3, 4] it is possible to have other sensible realizations which go beyond the space of square integrable functions but still have a semibounded Hamiltonian.