wip - dependent expr simpliifer

- simplify iterator over current indices
- add more simplifiers used by asserted_formulas
- improve diagnostics printing

src/ast/simplifiers/solve_eqs.h

@@ -32,6 +32,10 @@ namespace euf {
         struct stats {
             unsigned m_num_steps = 0;
             unsigned m_num_elim_vars = 0;
+            void reset() {
+                m_num_steps = 0;
+                m_num_elim_vars = 0;
+            }
         };
 
         struct config {
@@ -78,5 +82,7 @@ namespace euf {
 
         void collect_statistics(statistics& st) const override;
 
+        void reset_statistics() override { m_stats.reset(); }
+
     };
 }