. Let X and Y be topological spaces and f : X → Y be a continuous function. We are interested in finding points of X and Y at which f is open. We will show that if X is developable, the set of points of openness of f in X is a Gδ subset of X. If X is developable and f is closed, then the set of points of openness of f in Y is a Gδ subset of Y. These will extend some results of S. Levi.

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