+/* Expand the constraint "c" into "v". The initial "dim" dimensions
+ * are the same, but "v" may have more divs than "c" and the divs of "c"
+ * may appear in different positions in "v".
+ * The number of divs in "c" is given by "n_div" and the mapping
+ * of divs in "c" to divs in "v" is given by "div_map".
+ *
+ * Although it shouldn't happen in practice, it is theoretically
+ * possible that two or more divs in "c" are mapped to the same div in "v".
+ * These divs are then necessarily the same, so we simply add their
+ * coefficients.
+ */