A fixed point theorem for branched covering maps of the plane

Original · EN

It is known that every homeomorphism of the plane has a fixed point in a non-separating, invariant subcontinuum. Easy examples show that a branched covering map of the plane can be periodic point free. In this paper we show that any branched covering map of the plane of degree with absolute value at most two, which has an invariant, non-separating continuum Y, either has a fixed point in Y, or Y contains a minimal (by inclusion among invariant continua), fully invariant, non-separating subcontinuum X. In the latter case, f has to be of degree -2 and X has exactly three fixed prime ends, one corresponding to an outchannel and the other two to inchannels.