  The Alladi-Gordon identity plays an important role for the Alladi-Gordon
generalization of Schur's partition theorem. By using Joichi-Stanton's
insertion algorithm, we present an overpartition interpretation for the
Alladi-Gordon key identity. Based on this interpretation, we further obtain a
combinatorial proof of the Alladi-Gordon key identity by establishing an
involution on the underlying set of overpartitions.
