diff --git a/class/LogicUtils.php b/class/LogicUtils.php
index ab7420e..068adf5 100644
--- a/class/LogicUtils.php
+++ b/class/LogicUtils.php
@@ -48,6 +48,9 @@ class LogicUtils
             }
         } else {
             $numa_str = self::extend($numa_str, $base, $digits, false);
+            if (($rep === "c") && ($numa_str[0] >= ($base / 2))) {
+                $numa_str = str_pad($numa_str, 1, "0", STR_PAD_LEFT);
+            }
         }
         return $numa_str;
     }
diff --git a/class/Tasks/LogicFunctionTask.php b/class/Tasks/LogicFunctionTask.php
index 701a16c..11fa95f 100644
--- a/class/Tasks/LogicFunctionTask.php
+++ b/class/Tasks/LogicFunctionTask.php
@@ -14,7 +14,11 @@ class LogicFunctionTask extends LogicTaskBase
         if (!$this->hasFlag("dnf")) {
             $this->setCorrectAnswer($this->getLogicFunction()->getExpression());
         } else {
-            $this->setCorrectAnswer($this->getLogicFunction()->toDNF());
+            $dnf = $this->getLogicFunction()->toDNF();
+            if ($dnf === "") {
+                $dnf = "0";
+            }
+            $this->setCorrectAnswer($dnf);
         }
     }
 
diff --git a/class/Tasks/LogicTaskBase.php b/class/Tasks/LogicTaskBase.php
index 3317a4a..d1d945c 100644
--- a/class/Tasks/LogicTaskBase.php
+++ b/class/Tasks/LogicTaskBase.php
@@ -89,10 +89,6 @@ class LogicTaskBase extends PicturedTask
         $this->lf = LogicFunction::genRandomDNF(LuaUtils::l2pA($input_vars));
     }
 
-    public function getFunctionAsDNF(): string {
-        return $this->lf->toDNF();
-    }
-
     public function setLogicFunctionExpr(string $expr, array $input_vars = []): void {
         $this->lf = new LogicFunction($expr, LuaUtils::l2pA($input_vars));
     }