Mirrors and plane tessellations where some of its preferite themes but symmetry is used almost in any of his works .
Concerning plane tiling he got interested in them after a visit to Alhambra mosaics in Spain and afterward he explored systematically all 17 ways to fill the plane with the same repeating pattern.
He didn't have a formal mathematical background and worked always visually as an artist.He perhaps wouldn't be able to follow the usual way to present such plane patterns with combinations of trasformations and cryptic names like p4m,cm,etc. He wrote a wonderful book where he explained his tessellations in his way.