fact: Definition cell_center (c : cell) := midpoint (midpoint (seq.last dummy_pt (left_pts c)) (head dummy_pt (right_pts c))) (midpoint (head dummy_pt (left_pts c)) (seq.last dummy_pt (right_pts c))).
imports: mathcomp(all_ssreflect) ZArith QArith List String OrderedType OrderedTypeEx FMapAVL