Giuseppe GAETA Reduction and Equivariant Branching Lemma: Dynamical Systems, Evolution PDEs, and Gauge Theories (67K, Plain TeX) ABSTRACT. One of the simplest yet most useful tools in equivariant bifurcation theory is the so called "Equivariant Branching Lemma" (EBL in the following) of Cicogna nad Vanderbauwhede. The purpose of the present note is to extend the EBL to gauge symmetries and gauge-symmetric problems; this will be done by looking at gauge symmetries as a specific class of Lie-point symmetries in an appropriate space. We will also obtain a weaker result (reduction lemma) for evolution PDEs.