
Sunday night seems the right time to post a gallery of (I hope!) every one of Catriona's geometry puzzles.
https://notes.mathforge.org/notes/published/puzzle+gallery
Give it a moment to load ... there's a *lot* of them!

Using the matrix constructor for making morphisms of free modules now supports more cases, in particular: sage: M = matrix(QQ, entries=7, row_keys=[1, 2, 3]); M Generic endomorphism of Free module ...