diff --git a/src/ast/rewriter/poly_rewriter.h b/src/ast/rewriter/poly_rewriter.h
index 5269f25a8..8cbc7f864 100644
--- a/src/ast/rewriter/poly_rewriter.h
+++ b/src/ast/rewriter/poly_rewriter.h
@@ -112,6 +112,7 @@ public:
     bool is_mul(func_decl * f) const { return is_decl_of(f, get_fid(), mul_decl_kind()); }
     bool is_times_minus_one(expr * n, expr*& r) const;
     bool is_var_plus_ground(expr * n, bool & inv, var * & v, expr_ref & t);
+    bool is_zero(expr* e) const;
 
 
     br_status mk_mul_core(unsigned num_args, expr * const * args, expr_ref & result) {
diff --git a/src/ast/rewriter/poly_rewriter_def.h b/src/ast/rewriter/poly_rewriter_def.h
index 6b747756c..731a0538a 100644
--- a/src/ast/rewriter/poly_rewriter_def.h
+++ b/src/ast/rewriter/poly_rewriter_def.h
@@ -64,6 +64,13 @@ expr * poly_rewriter<Config>::get_power_body(expr * t, rational & k) {
     return t;
 }
 
+template<typename Config>
+bool poly_rewriter<Config>::is_zero(expr* e) const {
+    rational v;
+    return is_numeral(e, v) && v.is_zero();
+}
+
+
 template<typename Config>
 expr * poly_rewriter<Config>::mk_mul_app(unsigned num_args, expr * const * args) { 
     switch (num_args) {
diff --git a/src/smt/proto_model/proto_model.cpp b/src/smt/proto_model/proto_model.cpp
index 9b218037e..725c9fc51 100644
--- a/src/smt/proto_model/proto_model.cpp
+++ b/src/smt/proto_model/proto_model.cpp
@@ -161,8 +161,10 @@ void proto_model::cleanup_func_interp(func_interp * fi, func_decl_set & found_au
                     continue;
                 }
                 func_decl * f = t->get_decl();
-                if (m_aux_decls.contains(f))
+                if (m_aux_decls.contains(f)) {
+                    TRACE("model_bug", tout << f->get_name() << "\n";);
                     found_aux_fs.insert(f);
+                }
                 expr_ref new_t(m_manager);
                 new_t = m_rewrite.mk_app(f, args.size(), args.c_ptr());
                 if (t != new_t.get())
@@ -180,9 +182,7 @@ void proto_model::cleanup_func_interp(func_interp * fi, func_decl_set & found_au
         }
     }
 
-    if (!cache.find(fi_else, a)) {
-        UNREACHABLE();
-    }
+    VERIFY(cache.find(fi_else, a));
 
     fi->set_else(a);
 }
diff --git a/src/smt/smt_model_generator.cpp b/src/smt/smt_model_generator.cpp
index 49e9083f2..953afd4b7 100644
--- a/src/smt/smt_model_generator.cpp
+++ b/src/smt/smt_model_generator.cpp
@@ -17,14 +17,14 @@ Revision History:
 
 --*/
 
-#include "smt/smt_context.h"
-#include "smt/smt_model_generator.h"
-#include "smt/proto_model/proto_model.h"
 #include "util/ref_util.h"
 #include "ast/for_each_expr.h"
 #include "ast/ast_ll_pp.h"
 #include "ast/ast_pp.h"
 #include "ast/ast_smt2_pp.h"
+#include "smt/smt_context.h"
+#include "smt/smt_model_generator.h"
+#include "smt/proto_model/proto_model.h"
 
 namespace smt {