Abstract. We give a short proof of an improved version of the E¤ros Open Mapping Principle via a shift-compactness theorem (also with a short proof), involving 'sequential analysis'rather than separability, deducing it from the Baire property in a general Baire-space setting (rather than under topological completeness). It is applicable to absolutely-analytic normed groups (which include complete metrizable topological groups), and via a Steinhaus-type Sum-set Theorem (also a consequence of the shift-compactness theorem) includes the classical Open Mapping Theorem (separable or otherwise).