## Sets of constant distance from a planar set.(English)Zbl 0244.54019

### MSC:

 54E35 Metric spaces, metrizability 57N05 Topology of the Euclidean $$2$$-space, $$2$$-manifolds (MSC2010) 57N15 Topology of the Euclidean $$n$$-space, $$n$$-manifolds ($$4 \leq n \leq \infty$$) (MSC2010)
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