Module docstring
{"### Lemmas about arithmetic operations and intervals. ","inv_mem_Ixx_iff, sub_mem_Ixx_iff ","add_mem_Ixx_iff_left ","add_mem_Ixx_iff_right ","sub_mem_Ixx_iff_left ","sub_mem_Ixx_iff_right ","sub_mem_Ixx_zero_right and sub_mem_Ixx_zero_iff_right; this specializes the previous
lemmas to the case of reflecting the interval. ","### Lemmas about disjointness of translates of intervals "}