this is from Munkres Topology and I'm confused about the extension of $j$ from $A$ to $A\cup C$ by the preceding lemma which is the below:
according to this lemma $C\cup A \times I$ should be normal but how we know it, what I'm missing?
2026-05-05 17:08:47.1778000927
some detail about Borsuk Lemma
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