A gnomon is a shape which, when added to a figure, yields a figure
that is similar to the original one. Gazalé~[4]
conjectured that if the gnomon is a regular polygon and the figure
to which it is added is a finite polygon then the gnomon is a
triangle or a square. We prove this conjecture to be correct.
Keywords: Gnomon, polygon, tesselation, spiral, discontinuous group action.