sentence1: the unfoldings have multiple pieces partly for practical reasons such as efficient packing into a rectangle of material , but mainly because little theory on unfolding nonconvex polyhedra is available , and thus heuristics must be used .
sentence2: multipiece unfoldings are used partly for practical reasons such as efficient area use , but mainly because little theory on unfolding nonconvex polyhedra is available , and thus heuristics must be used .