We prove that for the AKNS operator H(p, q) the Dirichlet spectrum det
ermines the pair (p, q) if (p, q) is given on the half-left (or half-r
ight) of the unit interval. In other words every pair of functions on
the left interval has, at most, one extension on the right interval to
a pair of functions that lie on one Dirichlet isospectral set.