diff --git a/src/rpn-test.hpp b/src/rpn-test.hpp
index 4c888a8..434a71c 100644
--- a/src/rpn-test.hpp
+++ b/src/rpn-test.hpp
@@ -1,91 +1,166 @@
+int cmp_strings_on_stack_top()
+{
+    // _stack sould have 2 strings at level 1 and 2
+    // this function removes these 2 entries
+    ostring* right =  (ostring*)_stack->pop_back();
+    ostring* left = (ostring*)_stack->pop_back();
+    return strncmp(left->_value, right->_value, min(left->_len, right->_len));
+}
+
 void sup(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) > 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) > 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp > 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void sup_eq(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) >= 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) >= 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp >= 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void inf(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) < 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) < 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp < 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void inf_eq(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) <= 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) <= 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp <= 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void diff(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) != 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) != 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp != 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void eq(void)
 {
     MIN_ARGUMENTS(2);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
-    ARG_MUST_BE_OF_TYPE(1, cmd_number);
 
-    number* right =  (number*)_stack->pop_back();
-    number* left = (number*)_stack->back();
+    // numbers
+    if (_stack->get_type(0) == cmd_number && _stack->get_type(1) == cmd_number)
+    {
+        number* right =  (number*)_stack->pop_back();
+        number* left = (number*)_stack->back();
 
-    if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) == 0)
-        mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        if (mpfr_cmp(left->_value.mpfr, right->_value.mpfr) == 0)
+            mpfr_set_si(left->_value.mpfr, 1, floating_t::s_mpfr_rnd);
+        else
+            mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+    }
+    // strings
+    else if (_stack->get_type(0) == cmd_string && _stack->get_type(1) == cmd_string)
+    {
+        int res_cmp = cmp_strings_on_stack_top();
+        number* res = (number*)_stack->allocate_back(number::calc_size(), cmd_number);
+        res->_value = (res_cmp == 0) ? 1L : 0L;
+    }
     else
-        mpfr_set_si(left->_value.mpfr, 0, floating_t::s_mpfr_rnd);
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void test_and(void)
diff --git a/test/08-test.txt b/test/08-test.txt
index 57b6913..82f4881 100644
--- a/test/08-test.txt
+++ b/test/08-test.txt
@@ -173,3 +173,71 @@ drop
 1 1 same
 -> stack should be 1
 drop
+
+# string >
+"a" "b" >
+-> stack should be 0
+drop
+"b" "a" >
+-> stack should be 1
+drop
+"a" "a" >
+-> stack should be 0
+drop
+
+# string >=
+"a" "b" >=
+-> stack should be 0
+drop
+"b" "a" >=
+-> stack should be 1
+drop
+"a" "a" >=
+-> stack should be 1
+drop
+
+# string <
+"a" "b" <
+-> stack should be 1
+drop
+"b" "a" <
+-> stack should be 0
+drop
+"a" "a" <
+-> stack should be 0
+drop
+
+# string <=
+"a" "b" <=
+-> stack should be 1
+drop
+"b" "a" <=
+-> stack should be 0
+drop
+"a" "a" <=
+-> stack should be 1
+drop
+
+# string !=
+"a" "b" !=
+-> stack should be 1
+drop
+"a" "a" !=
+-> stack should be 0
+drop
+
+# string ==
+"a" "b" ==
+-> stack should be 0
+drop
+"a" "a" ==
+-> stack should be 1
+drop
+
+# string same
+"a" "b" same
+-> stack should be 0
+drop
+"a" "a" same
+-> stack should be 1
+drop