+/* Intermediate data per table. */
+struct workspace
+{
+ /* An array of n_layers integers which are used
+ to permute access into the factor_vars of each layer. */
+ int *control_idx;
+
+ /* An array of n_layers cell_containers which hold the union
+ of instances used respectively by each layer. */
+ struct cell_container *instances;
+
+ struct cell *root_cell;
+};