diff --git a/src/main/java/Main.java b/src/main/java/Main.java
index 63b0c9e..b46f711 100644
--- a/src/main/java/Main.java
+++ b/src/main/java/Main.java
@@ -2,6 +2,8 @@
 import java.util.Map;
 
 import constants.Types;
+import inference.InferenceRule;
+import inference.ProofSystem;
 import models.algebra.Type;
 import models.algebra.Variable;
 import models.terms.Dependency;
@@ -18,7 +20,13 @@
 
 	public static void main(String[] args) {
 		//
-		sandBox8();
+		sandBox();
+//		sandBox8();
+	}
+	
+	static void sandBox() {
+		InferenceRule rule = ProofSystem.argumentExtension;
+		System.out.println(rule.getMissingVariables());
 	}
 	
 	
diff --git a/src/main/java/inference/InferenceRule.java b/src/main/java/inference/InferenceRule.java
index 97e0056..c7d7755 100644
--- a/src/main/java/inference/InferenceRule.java
+++ b/src/main/java/inference/InferenceRule.java
@@ -23,7 +23,8 @@
 	protected MetaFormula conclusion;
 	protected InferenceOrderConstraint defaultOrderConstraint;
 	
-	protected List<MetaVariable> missingVariables;
+	@Getter
+	protected List<MetaVariable> missingVariables = new ArrayList<>();
 	
 	protected InferenceRule(String name) {
 		this.name = name;
@@ -45,6 +46,7 @@
 		this(name, assumptions, conclusion, null);
 	}
 	
+	
 	public Set<Formula> derive(List<Formula> assumptions) {
 		return derive(assumptions, MatchConstraint.createDefault());
 	}
@@ -80,6 +82,7 @@
 		return matchResult;
 	}
 	
+	
 //	public Set<Formula> apply(Set<Formula> formulas, Set<RDLTerm> existTerms) {
 //		List<List<Formula>> matchFormulas = new ArrayList<>();
 //		List<List<RDLTerm>> matchTerms = new ArrayList<>();