  The line-soliton solutions of the Kadomtsev--Petviashvili (KP) equation are
investigated in this article using the tau-function formalism. In particular,
the Wronskian and the Grammian forms of the tau-function are discussed, and the
equivalence of these two forms are established. Furthermore, the interaction
properties of two special types of 2-soliton solutions of the KP equation are
studied in details.
