The inverse Sturm-Liouville problem with mixed boundary conditions
  Consider the operator $H\p=-\p''+q\p=\l\p$, $\p(0)=0$, $\p'(1)+b\p(1)=0$ acting in $L^2(0,1)$, where $q\in L^2(0,1)$ is a real potential. Let $\l_n(q,b)$, $n\ge 0$, be the eigenvalues of $H$ and $\n_n(q,b)$ be the so-called norming constants. We give a complete characterization of all spectral data $(\{\l_n\}_0^\iy;\{\n_n\}_0^\iy)$ that correspond to $(q;b)\in L^2(0,1)\ts\R$. If $b$ is fixed, then we obtain a similar characterization and parameterize the iso-spectral manifolds. 
Dmitri Chelkak, Evgeny Korotyaev