diff --git a/adeterminize/src/rhdpda/RhdpdaUtils.cpp b/adeterminize/src/rhdpda/RhdpdaUtils.cpp
index fa13248787d53611a068e57eb7223ca63e495a5d..eb71d962f2c0e585d35ee1dcab08e413246a13a4 100644
--- a/adeterminize/src/rhdpda/RhdpdaUtils.cpp
+++ b/adeterminize/src/rhdpda/RhdpdaUtils.cpp
@@ -4,7 +4,7 @@ namespace determinization {
 namespace rhdpda {
 
 
-const Symbol RhdpdaUtils::BOTTOM_OF_STACK_SYMBOL("_"); // TODO specialni symbol pro dno zasobniku zpusobuje chybu
+const Symbol RhdpdaUtils::BOTTOM_OF_STACK_SYMBOL("⊥");
 
 
 string RhdpdaUtils::buildPairName(const StateSymbolPair& pair)
diff --git a/examples/automaton/RHDPDA1.xml b/examples/automaton/RHDPDA1.xml
index b6ee03f349e36ed2ceb39723ece9befd8b101d90..ca6a04ba9adcf5b4729e71faf2d9fbfbdba0b999 100644
--- a/examples/automaton/RHDPDA1.xml
+++ b/examples/automaton/RHDPDA1.xml
@@ -13,7 +13,7 @@
   <stackAlphabet>
     <symbol>a</symbol>
     <symbol>x</symbol>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </stackAlphabet>
   <transitions>
     <transition>
@@ -21,11 +21,11 @@
       <input>a</input>
       <to>1</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
         <symbol>x</symbol>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -33,10 +33,10 @@
       <input>b</input>
       <to>3</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -130,10 +130,10 @@
       <input>a</input>
       <to>ERR</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -141,10 +141,10 @@
       <input>b</input>
       <to>ERR</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -152,10 +152,10 @@
       <input>a</input>
       <to>ERR</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -185,10 +185,10 @@
       <input>b</input>
       <to>ERR</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -218,7 +218,7 @@
     <state>0</state>
   </initialStates>
   <startSymbols>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </startSymbols>
   <finalStates>
     <state>3</state>
diff --git a/examples/automaton/RHDPDA2.xml b/examples/automaton/RHDPDA2.xml
index 772fa5879085e209e8251b2968d3e9a173e815f5..06f09818e2b3bf0b63dad4dc87b593fd26690dc9 100644
--- a/examples/automaton/RHDPDA2.xml
+++ b/examples/automaton/RHDPDA2.xml
@@ -13,7 +13,7 @@
   <stackAlphabet>
     <symbol>a</symbol>
     <symbol>x</symbol>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </stackAlphabet>
   <transitions>
     <transition>
@@ -106,7 +106,7 @@
     <state>0</state>
   </initialStates>
   <startSymbols>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </startSymbols>
   <finalStates>
     <state>3</state>
diff --git a/examples/automaton/RHDPDA3.xml b/examples/automaton/RHDPDA3.xml
index 8ca65104a14e75ce1cfee6e26b00cfbef215873d..2d7b2966bb3075c260fe0612beff9f9b893ed500 100644
--- a/examples/automaton/RHDPDA3.xml
+++ b/examples/automaton/RHDPDA3.xml
@@ -8,7 +8,7 @@
   </inputAlphabet>
   <stackAlphabet>
     <symbol>a</symbol>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </stackAlphabet>
   <transitions>
     <transition>
@@ -16,11 +16,11 @@
       <input>a</input>
       <to>1</to>
       <pop>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </pop>
       <push>
         <symbol>a</symbol>
-        <symbol>_</symbol>
+        <symbol>⊥</symbol>
       </push>
     </transition>
     <transition>
@@ -37,7 +37,7 @@
     <state>0</state>
   </initialStates>
   <startSymbols>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </startSymbols>
   <finalStates>
     <state>0</state>
diff --git a/examples/automaton/RHDPDA4.xml b/examples/automaton/RHDPDA4.xml
index 91a822d4ee09a5a21ca9ae1d6eb799a0b99d2b04..383daf6e1a430f490bb3960a1ef5334e62d58f64 100644
--- a/examples/automaton/RHDPDA4.xml
+++ b/examples/automaton/RHDPDA4.xml
@@ -8,7 +8,7 @@
   </inputAlphabet>
   <stackAlphabet>
     <symbol>a</symbol>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </stackAlphabet>
   <transitions>
     <transition>
@@ -34,7 +34,7 @@
     <state>0</state>
   </initialStates>
   <startSymbols>
-    <symbol>_</symbol>
+    <symbol>⊥</symbol>
   </startSymbols>
   <finalStates>
     <state>0</state>