add utilities for purification

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/qe/qe_term_graph.h

@@ -122,6 +122,19 @@ namespace qe {
          */
         expr_ref_vector get_ackerman_disequalities();
 
+        /**
+         * Produce a model-based partition.
+         */
+        vector<expr_ref_vector> get_partition(model& mdl);
+
+        /**
+         * Extract shared occurrences of terms whose sort are 
+         * fid, but appear in a context that is not fid.
+         * for example f(x + y) produces the shared occurrence
+         * x + y when f is uninterpreted and x + y has sort Int or Real.
+         */
+        expr_ref_vector shared_occurrences(family_id fid);
+
     };
 
 }