Every mathematician is influenced, directly or indirectly, by every other mathematician.
Even in the case of direct influence, there is an explicit and implicit influence, and in the latter case, we are not always aware of it. Implicitly, because he was such a great teacher, who taught me PDEs so well, and at the same time how to do mathematics. Explicitly, because he was the first one to tell me about Joseph Bernstein's theory of holonomic systems, that was crucial for so-called WZ theory. Iossif Polterovich has found far-reaching extensions of the method initiated in this note. Read Iossif Polterovich's very interesting paper .