Do missing renames of "cross product" to "Cartesian product"
Do missing renames of "cross product" to "Cartesian product"

We did a mass rename from "cross product" to the more
common term "Cartesian product".  However, that mass rename
missed a few cases.

This commit fixes cases that were accidentally missed
in the previous mass rename.

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

metamath/set.mm,metamath/set.mm,metamath/set.mm