Substructures of a pair

From CS2800 wiki

If [math]x' [/math] and [math]y' [/math] are substructures of [math]x [/math] and [math]y [/math] respectively, then [math](x',y') [/math], [math](x,y') [/math] and [math](x',y) [/math] can all be considered substructures of [math](x,y) [/math]: they must all have been shown to be in [math]X \href{/cs2800/wiki/index.php/%5Ctimes}{\times} X [/math] before we could show that [math](x,y) \href{/cs2800/wiki/index.php/%E2%88%88}{∈} X \href{/cs2800/wiki/index.php/%5Ctimes}{\times} X [/math].