Proof: Let {Uα} be an open cover of X×Y. For each x∈X, the space {x}×Y≅Y is compact, so let it be covered by finitely many Ux1,...,Uxn with nontrivial intersection with {x}×Y, and let Wx=∩π1(Uxi). Then {Wx}x∈X is an open cover of X, so let A be a locally finite open refinement covering X. For each A∈A, finitely many Ux1,...,Uxn cover A×Y⊆Wx×Y (for some x), so let CA={(A×Y)∩Uxi}. We claim C=∪A∈ACA is a locally finite open refinement of {Uα} covering X×Y.
Every element of each CA is contained in some Uα, so C is clearly a refinement. As well, given z=x×y∈X×Y, let x∈A∈A so that z∈A×Y=∪CA implying z is contained in an element of CA and now C covers X. Finally, choose a neighborhood U of x intersecting only finitely many members Ai∈A. Then U×Y is a neighborhood of z that can intersect only among the members of CAi, all of which are finite. Therefore C is locally finite and X×Y is paracompact. ◻
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