  Fox conjectured the Alexander polynomial of an alternating knot is
trapezoidal, i.e. the coefficients first increase, then stabilize and finally
decrease in a symmetric way. Recently, Hirasawa and Murasugi further
conjectured a relation between the number of the stable coefficients in the
Alexander polynomial and the signature invariant. In this paper we prove the
Hirasawa-Murasugi conjecture for two-bridge knots.
