  It is well known that in every inverse semigroup the binary operation and the
unary operation of inversion satisfy the following three identities: [\quad
x=(xx')x \qquad \quad (xx')(y'y)=(y'y)(xx') \qquad \quad (xy)z=x(yz"). ] The
goal of this note is to prove the converse, that is, we prove that an algebra
of type $<2,1>$ satisfying these three identities is an inverse semigroup and
the unary operation coincides with the usual inversion on such semigroups.
