Local Problems, Planar Local Problems and Linear Time. - Régis Barbanchon; Etienne Grandjean (CSL, 2002)

The Minimal Logically-Defined NP-Complete Problem. - Régis Barbanchon; Etienne Grandjean (STACS, 2004)

On unique graph 3-colorability and parsimonious reductions in the plane. - Régis Barbanchon (Theor. Comput. Sci., 2004)