diff --git a/src/kernel/arith/arith.cpp b/src/kernel/arith/arith.cpp
index 211bd47a7..a0bad8b7e 100644
--- a/src/kernel/arith/arith.cpp
+++ b/src/kernel/arith/arith.cpp
@@ -13,32 +13,27 @@ namespace lean {
 
 class int_type_value : public value {
 public:
-    static char const * g_kind;
     virtual ~int_type_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return Type(); }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const { return false; }
-    virtual bool operator==(value const & other) const { return other.kind() == kind(); }
+    virtual bool operator==(value const & other) const { return dynamic_cast<int_type_value const*>(&other) != nullptr; }
     virtual void display(std::ostream & out) const { out << "Int"; }
     virtual format pp() const { return format("Int"); }
     virtual unsigned hash() const { return 41; }
 };
-
-char const * int_type_value::g_kind = "int";
 expr const Int = mk_value(*(new int_type_value()));
 expr mk_int_type() { return Int; }
 
 class int_value_value : public value {
     mpz m_val;
 public:
-    static char const * g_kind;
     int_value_value(mpz const & v):m_val(v) {}
     virtual ~int_value_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return Int; }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const { return false; }
     virtual bool operator==(value const & other) const {
-        return other.kind() == kind() && m_val == static_cast<int_value_value const &>(other).m_val;
+        int_value_value const * _other = dynamic_cast<int_value_value const*>(&other);
+        return _other && _other->m_val == m_val;
     }
     virtual void display(std::ostream & out) const { out << m_val; }
     virtual format pp() const { return format(m_val); }
@@ -46,14 +41,12 @@ public:
     mpz const & get_num() const { return m_val; }
 };
 
-char const * int_value_value::g_kind = "int_num";
-
 expr mk_int_value(mpz const & v) {
     return mk_value(*(new int_value_value(v)));
 }
 
 bool is_int_value(expr const & e) {
-    return is_value(e) && to_value(e).kind() == int_value_value::g_kind;
+    return is_value(e) && dynamic_cast<int_value_value const *>(&to_value(e)) != nullptr;
 }
 
 mpz const & int_value_numeral(expr const & e) {
@@ -65,14 +58,12 @@ template<char const * Name, unsigned Hash, typename F>
 class int_bin_op : public value {
     expr m_type;
 public:
-    static char const * g_kind;
     int_bin_op() {
         m_type = Int >> (Int >> Int);
     }
     virtual ~int_bin_op() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return m_type; }
-    virtual bool operator==(value const & other) const { return other.kind() == kind(); }
+    virtual bool operator==(value const & other) const { return dynamic_cast<int_bin_op const*>(&other) != nullptr; }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const {
         if (num_args == 3 && is_int_value(args[1]) && is_int_value(args[2])) {
             r = mk_int_value(F()(int_value_numeral(args[1]), int_value_numeral(args[2])));
@@ -86,8 +77,6 @@ public:
     virtual unsigned hash() const { return Hash; }
 };
 
-template<char const * Name, unsigned Hash, typename F> char const * int_bin_op<Name, Hash, F>::g_kind = Name;
-
 constexpr char int_add_name[] = "+";
 struct int_add_eval { mpz operator()(mpz const & v1, mpz const & v2) { return v1 + v2; }; };
 typedef int_bin_op<int_add_name, 43, int_add_eval> int_add_value;
@@ -111,14 +100,12 @@ MK_BUILTIN(int_div_fn, int_div_value);
 class int_le_value : public value {
     expr m_type;
 public:
-    static char const * g_kind;
     int_le_value() {
         m_type = Int >> (Int >> Bool);
     }
     virtual ~int_le_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return m_type; }
-    virtual bool operator==(value const & other) const { return other.kind() == kind(); }
+    virtual bool operator==(value const & other) const { return dynamic_cast<int_le_value const*>(&other) != nullptr; }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const {
         if (num_args == 3 && is_int_value(args[1]) && is_int_value(args[2])) {
             r = mk_bool_value(int_value_numeral(args[1]) <= int_value_numeral(args[2]));
@@ -131,7 +118,6 @@ public:
     virtual format pp() const { return format("Le"); }
     virtual unsigned hash() const { return 67; }
 };
-char const * int_le_value::g_kind = "<=";
 MK_BUILTIN(int_le_fn, int_le_value);
 
 MK_CONSTANT(int_ge_fn, name(name("int"), "Ge"));
diff --git a/src/kernel/builtin.cpp b/src/kernel/builtin.cpp
index 355d738d8..308fb3b3f 100644
--- a/src/kernel/builtin.cpp
+++ b/src/kernel/builtin.cpp
@@ -60,17 +60,14 @@ static char const * g_Bool_str = "Bool";
 static format g_Bool_fmt(g_Bool_str);
 class bool_type_value : public value {
 public:
-    static char const * g_kind;
     virtual ~bool_type_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return Type(); }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const { return false; }
-    virtual bool operator==(value const & other) const { return other.kind() == kind(); }
+    virtual bool operator==(value const & other) const { return dynamic_cast<bool_type_value const*>(&other) != nullptr; }
     virtual void display(std::ostream & out) const { out << g_Bool_str; }
     virtual format pp() const { return g_Bool_fmt; }
     virtual unsigned hash() const { return 17; }
 };
-char const * bool_type_value::g_kind = g_Bool_str;
 expr const Bool = mk_value(*(new bool_type_value()));
 expr mk_bool_type() { return Bool; }
 // =======================================
@@ -88,14 +85,13 @@ static format g_false_fmt(g_false_str);
 class bool_value_value : public value {
     bool m_val;
 public:
-    static char const * g_kind;
     bool_value_value(bool v):m_val(v) {}
     virtual ~bool_value_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return Bool; }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const { return false; }
     virtual bool operator==(value const & other) const {
-        return other.kind() == kind() && m_val == static_cast<bool_value_value const &>(other).m_val;
+        bool_value_value const * _other = dynamic_cast<bool_value_value const*>(&other);
+        return _other && _other->m_val == m_val;
     }
     virtual void display(std::ostream & out) const { out << (m_val ? g_true_str : g_false_str); }
     virtual format pp(bool unicode) const {
@@ -108,14 +104,13 @@ public:
     virtual unsigned hash() const { return m_val ? 3 : 5; }
     bool get_val() const { return m_val; }
 };
-char const * bool_value_value::g_kind = "BoolValue";
 expr const True  = mk_value(*(new bool_value_value(true)));
 expr const False = mk_value(*(new bool_value_value(false)));
 expr mk_bool_value(bool v) {
     return v ? True : False;
 }
 bool is_bool_value(expr const & e) {
-    return is_value(e) && to_value(e).kind() == bool_value_value::g_kind;
+    return is_value(e) && dynamic_cast<bool_value_value const *>(&to_value(e)) != nullptr;
 }
 bool to_bool(expr const & e) {
     lean_assert(is_bool_value(e));
@@ -136,14 +131,12 @@ static format g_ite_fmt(g_ite_name);
 class ite_fn_value : public value {
     expr m_type;
 public:
-    static char const * g_kind;
     ite_fn_value() {
         expr A    = Const("A");
         // Pi (A: Type), bool -> A -> A -> A
         m_type = Pi({A, TypeU}, Bool >> (A >> (A >> A)));
     }
     virtual ~ite_fn_value() {}
-    char const * kind() const { return g_kind; }
     virtual expr get_type() const { return m_type; }
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const {
         if (num_args == 5 && is_bool_value(args[2])) {
@@ -159,12 +152,11 @@ public:
             return false;
         }
     }
-    virtual bool operator==(value const & other) const { return other.kind() == kind(); }
+    virtual bool operator==(value const & other) const { return dynamic_cast<ite_fn_value const*>(&other) != nullptr; }
     virtual void display(std::ostream & out) const { out << g_ite_name; }
     virtual format pp() const { return g_ite_fmt; }
     virtual unsigned hash() const { return 27; }
 };
-char const * ite_fn_value::g_kind = "ite";
 MK_BUILTIN(ite_fn, ite_fn_value);
 // =======================================
 
diff --git a/src/kernel/builtin.h b/src/kernel/builtin.h
index 3c7104df9..8b6721ff3 100644
--- a/src/kernel/builtin.h
+++ b/src/kernel/builtin.h
@@ -161,7 +161,7 @@ expr mk_##Name() {                                                      \
     return r;                                                           \
 }                                                                       \
 bool is_##Name(expr const & e) {                                        \
-    return is_value(e) && to_value(e).kind() == ClassName::g_kind;      \
+    return is_value(e) && dynamic_cast<ClassName const *>(&to_value(e)) != nullptr; \
 }
 
 /**
diff --git a/src/kernel/expr.h b/src/kernel/expr.h
index df8f7e719..03d45b056 100644
--- a/src/kernel/expr.h
+++ b/src/kernel/expr.h
@@ -203,7 +203,6 @@ class value {
 public:
     value():m_rc(0) {}
     virtual ~value() {}
-    virtual char const * kind() const = 0;
     virtual expr get_type() const = 0;
     virtual bool normalize(unsigned num_args, expr const * args, expr & r) const = 0;
     virtual bool operator==(value const & other) const = 0;