24593 Paul Bell: A note on the emptiness of semigroup intersections.
Internet ca. 2008, 4p.

24622 Vesa Halava/Tero Harju: Mortality in matrix semigroups.
TUCS 361 (2000), 8p.

24585 Jody Lockhart: The Skolem problem for 2x2 matrices, arctangents
and recursive solvability. Alb. J. Math. 1/1 (2007), 13-16.