Sequential unions of core-compact spaces commute with products

Abstract

We show that given two sequences of core-compact spaces \[ X_0 \hookrightarrow \dots \hookrightarrow X_n \hookrightarrow \dots \quad \text{and} \quad Y_0 \hookrightarrow \dots \hookrightarrow Y_n \hookrightarrow \dots \] with continuous injective transition maps, the union topology of the products \[ \cup_n (X_n \times Y_n) = \left(\cup_n X_n\right) \times \left( \cup_n Y_n \right) \] is the product topology of the unions.