Uniqueness in Rough Almost Complex Structures and Differential Inequalities

We prove that for almost complex structures of H\"older class at least 1/2, any J-holomorphic disc, that is constant on some non empty open set, is constant. This is in striking contrast with well known, trivial, non-uniqueness results. We also investigate uniqueness questions (do vanishing on some open set, or vanishing to infinite order, or having a non isolated zero, imply vanishing) in connection with differential inequalities that arise in the theory of almost complex manifolds. The case of vector valued functions is different from the case of scalar valued functions.