Definition: a flow line (of 2D vector field) is a curve that vector field is tangent everywhere to it. If the vector field is zero at some point (singular point) the definition is ambiguous. Does this mean a flow line that reaches a singular point should terminate there?
An example from physics: electric field lines of two positive same charges has a singular point at the middle of connecting line of two charges. Now does the field line statrting from one of the charges in the direction of the connecting line, terminate at the singular point? Because usually we assume that an electric field line cannot terminate at empty space?