We will represent the inter-boson interaction by a pairwise, repulsive potential
Vint(|ri−rj|)={∞|ri−rj|≤a0|ri−rj|>awhere a is the so-called hard-core diameter of the bosons. Clearly, Vint(|ri−rj|) is zero if the bosons are separated by a distance |ri−rj| greater than a but infinite if they attempt to come within a distance |ri−rj|≤a.