@article{Belleville1992ProbingPM,
title={Probing Polygons Minimally Is Hard},
author={Patrice Belleville and Thomas C. Shermer},
journal={Comput. Geom.},
year={1992},
volume={2},
pages={255-265}
}

Belleville, P. and T.C. Shermer, Probing polygons minimally is hard, Computational Geometry: Theory and Applications 2 (1993) 255-265. Let r be a set of convex unimodal polygons in fixed position and orientation. We prove that the problem of determining whether k finger probes are sufficient to distinguish among the polygons in f is NP-complete for two types of finger probes. This implies that the same results hold for most interesting classes of polygons on which finger probes can be used.