Passage, blockade, sink and source of a planar dynamical system (Q1200099)

For a planar dynamical system, the author introduces such notion as passage, blockade, sink and source of a multi-connected region \(G\). He studies relations between indices of critical points in \(G\) and the numbers of points where trajectories are internally and externally tangent to the boundary of \(G\). There are three theorems on non-existence and existence of closed orbits and some number of examples as well as discussion of results and a conjecture on a number of passages.