diff --git a/src/ast/ast.cpp b/src/ast/ast.cpp
index f164d6a4f..9ce1b582d 100644
--- a/src/ast/ast.cpp
+++ b/src/ast/ast.cpp
@@ -1934,8 +1934,7 @@ sort * ast_manager::substitute(sort* s, unsigned n, sort * const * src, sort * c
     vector<parameter> ps;
     bool change = false;
     sort_ref_vector sorts(*this);
-    for (unsigned i = 0; i < s->get_num_parameters(); ++i) {
-        parameter const& p = s->get_parameter(i);
+    for (parameter const& p : s->parameters()) {
         if (p.is_ast()) {
             SASSERT(is_sort(p.get_ast()));
             change = true;
@@ -2330,8 +2329,8 @@ bool ast_manager::is_label_lit(expr const * n, buffer<symbol> & names) const {
         return false;
     }
     func_decl const * decl = to_app(n)->get_decl();
-    for (unsigned i = 0; i < decl->get_num_parameters(); i++)
-        names.push_back(decl->get_parameter(i).get_symbol());
+    for (parameter const& p : decl->parameters()) {
+        names.push_back(p.get_symbol());
     return true;
 }
 
@@ -2928,8 +2927,8 @@ bool ast_manager::is_quant_inst(expr const* e, expr*& not_q_or_i, ptr_vector<exp
         not_q_or_i = to_app(e)->get_arg(0);
         func_decl* d = to_app(e)->get_decl();
         SASSERT(binding.empty());
-        for (unsigned i = 0; i < d->get_num_parameters(); ++i) {
-            binding.push_back(to_expr(d->get_parameter(i).get_ast()));
+        for (parameter const& p : d->parameters()) {
+            binding.push_back(to_expr(p.get_ast()));
         }
         return true;
     }
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 7cd1dff93..364be8a77 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -273,6 +273,14 @@ public:
     parameter const * get_parameters() const { return m_parameters.begin(); }
     bool private_parameters() const { return m_private_parameters; }
 
+    struct iterator {
+        decl_info const& d;
+        iterator(decl_info const& d) : d(d) {}
+        parameter const* begin() const { return d.get_parameters(); }
+        parameter const* end() const { return begin() + d.get_num_parameters(); }
+    };
+    iterator parameters() const { return iterator(*this); }
+
     unsigned hash() const;
     bool operator==(decl_info const & info) const;
 };
@@ -571,6 +579,16 @@ public:
     parameter const & get_parameter(unsigned idx) const { return m_info->get_parameter(idx); }
     parameter const * get_parameters() const { return m_info == nullptr ? nullptr : m_info->get_parameters(); }
     bool private_parameters() const { return m_info != nullptr && m_info->private_parameters(); }
+
+    struct iterator {
+        decl const& d;
+        iterator(decl const& d) : d(d) {}
+        parameter const* begin() const { return d.get_parameters(); }
+        parameter const* end() const { return begin() + d.get_num_parameters(); }
+    };
+    iterator parameters() const { return iterator(*this); }
+
+
 };
 
 // -----------------------------------
@@ -2401,11 +2419,7 @@ public:
     }
 
     void reset() {
-        ptr_buffer<ast>::iterator it  = m_to_unmark.begin();
-        ptr_buffer<ast>::iterator end = m_to_unmark.end();
-        for (; it != end; ++it) {
-            reset_mark(*it);
-        }
+        for (ast* a : m_to_unmark) reset_mark(a); 
         m_to_unmark.reset();
     }
 
diff --git a/src/ast/datatype_decl_plugin.cpp b/src/ast/datatype_decl_plugin.cpp
index d3704a84a..284c4df93 100644
--- a/src/ast/datatype_decl_plugin.cpp
+++ b/src/ast/datatype_decl_plugin.cpp
@@ -692,6 +692,7 @@ namespace datatype {
         }
         unsigned num_well_founded = 0, id = 0;
         bool changed;
+        ptr_vector<sort> subsorts;
         do {
             changed = false;
             for (unsigned tid = 0; tid < num_types; tid++) {
@@ -701,23 +702,25 @@ namespace datatype {
                 sort* s = sorts[tid];
                 def const& d = get_def(s);
                 for (constructor const* c : d) {
-                    bool found_nonwf = false;
                     for (accessor const* a : *c) {
-                        if (sort2id.find(a->range(), id) && !well_founded[id]) {
-                            found_nonwf = true;
-                            break;
+                        subsorts.reset();
+                        get_subsorts(a->range(), subsorts);
+                        for (sort* srt : subsorts) {
+                            if (sort2id.find(srt, id) && !well_founded[id]) {
+                                goto next_constructor;
+                            }
                         }
                     }
-                    if (!found_nonwf) {
-                        changed = true;
-                        well_founded[tid] = true;
-                        num_well_founded++;
-                        break;
-                    }
+                    changed = true;
+                    well_founded[tid] = true;
+                    num_well_founded++;
+                    break;
+                next_constructor:
+                    ;
                 }
             }
         } 
-        while(changed && num_well_founded < num_types);
+        while (changed && num_well_founded < num_types);
         return num_well_founded == num_types;
     }
 
@@ -727,8 +730,7 @@ namespace datatype {
 
     void util::get_subsorts(sort* s, ptr_vector<sort>& sorts) const {
         sorts.push_back(s);
-        for (unsigned i = 0; i < s->get_num_parameters(); ++i) {
-            parameter const& p = s->get_parameter(i);
+        for (parameter const& p : s->parameters()) {
             if (p.is_ast() && is_sort(p.get_ast())) {
                 get_subsorts(to_sort(p.get_ast()), sorts);
             }
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index cd8571a95..00ba93ccb 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -376,8 +376,7 @@ bool seq_decl_plugin::match(ptr_vector<sort>& binding, sort* s, sort* sP) {
     if (s->get_family_id() == sP->get_family_id() &&
         s->get_decl_kind() == sP->get_decl_kind() &&
         s->get_num_parameters() == sP->get_num_parameters()) {
-        for (unsigned i = 0; i < s->get_num_parameters(); ++i) {
-            parameter const& p = s->get_parameter(i);
+        for (parameter const& p : s->parameters()) {
             if (p.is_ast() && is_sort(p.get_ast())) {
                 parameter const& p2 = sP->get_parameter(i);
                 if (!match(binding, to_sort(p.get_ast()), to_sort(p2.get_ast()))) return false;