📚 Recommended Mathematics Books

Topology (Munkres)  |  General Topology (Engelking)  |  Counterexamples in Topology  |  Rudin's Analysis

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Having a funcoid $latex f$ I defined what I call interior funcoid $latex f^\circ$. See this PDF file for a few equivalent definitions. Interior funcoid is a generalization of interior operator for a topological space. Interior funcoid is kinda dual funcoid.

Note that $latex f^{\circ\circ} = f$.