diff --git a/src/main/java/de/tla2b/analysis/UsedExternalFunctions.java b/src/main/java/de/tla2b/analysis/UsedExternalFunctions.java
index af6bb2e80bfeac1f8e458b961d285fb9943bdb45..6ee67e0f8919dc247cbe2e38927985ba8e1edcf6 100644
--- a/src/main/java/de/tla2b/analysis/UsedExternalFunctions.java
+++ b/src/main/java/de/tla2b/analysis/UsedExternalFunctions.java
@@ -19,16 +19,13 @@ public class UsedExternalFunctions extends AbstractASTVisitor implements BBuildI
 		return usedExternalFunctions;
 	}
 
-	public UsedExternalFunctions(ModuleNode moduleNode,
-	                             SpecAnalyser specAnalyser) {
+	public UsedExternalFunctions(ModuleNode moduleNode, SpecAnalyser specAnalyser) {
 		usedExternalFunctions = new HashSet<>();
-
 		visitAssumptions(moduleNode.getAssumptions());
 
 		for (OpDefNode def : specAnalyser.getUsedDefinitions()) {
 			visitDefinition(def);
 		}
-
 	}
 
 	@Override
@@ -62,7 +59,6 @@ public class UsedExternalFunctions extends AbstractASTVisitor implements BBuildI
 			usedExternalFunctions.add(EXTERNAL_FUNCTIONS.ASSERT);
 		}
 
-
 		ExprNode[] in = n.getBdedQuantBounds();
 		for (ExprNode exprNode : in) {
 			visitExprNode(exprNode);
@@ -73,5 +69,4 @@ public class UsedExternalFunctions extends AbstractASTVisitor implements BBuildI
 			visitExprOrOpArgNode(exprOrOpArgNode);
 		}
 	}
-
 }
diff --git a/src/main/java/de/tla2b/global/OperatorTypes.java b/src/main/java/de/tla2b/global/OperatorTypes.java
index 619a5c0045f3fdb5a9fbd0c72602e520775222c9..8d8c797ac3cda1f992bab48f352e3bc8f5d6d858 100644
--- a/src/main/java/de/tla2b/global/OperatorTypes.java
+++ b/src/main/java/de/tla2b/global/OperatorTypes.java
@@ -3,10 +3,11 @@ package de.tla2b.global;
 import tlc2.tool.ToolGlobals;
 
 import java.util.HashSet;
+import java.util.Set;
 
 public class OperatorTypes implements ToolGlobals, BBuildIns {
-	private static final HashSet<Integer> TLA_Predicate_Operators;
-	private static final HashSet<Integer> BBuiltIn_Predicate_Operators;
+	private static final Set<Integer> TLA_Predicate_Operators;
+	private static final Set<Integer> BBuiltIn_Predicate_Operators;
 
 	static {
 		TLA_Predicate_Operators = new HashSet<>();
diff --git a/src/main/java/de/tla2b/output/TypeVisitorInterface.java b/src/main/java/de/tla2b/output/TypeVisitorInterface.java
index 01ad7af9bcc6299cf08bf85d51f5c336f496a971..9c42f4bc486474a45176290d036186c889e38a48 100644
--- a/src/main/java/de/tla2b/output/TypeVisitorInterface.java
+++ b/src/main/java/de/tla2b/output/TypeVisitorInterface.java
@@ -2,7 +2,6 @@ package de.tla2b.output;
 
 import de.tla2b.types.*;
 
-
 public interface TypeVisitorInterface {
 
 	void caseIntegerType(IntType type);
diff --git a/src/main/java/de/tla2b/types/AbstractHasFollowers.java b/src/main/java/de/tla2b/types/AbstractHasFollowers.java
index ef6e146c1151a7bdb7e55fe0a61df0c3d5ab617b..5a91851128a3558949687258456adeec2298d7f8 100644
--- a/src/main/java/de/tla2b/types/AbstractHasFollowers.java
+++ b/src/main/java/de/tla2b/types/AbstractHasFollowers.java
@@ -3,17 +3,18 @@ package de.tla2b.types;
 import tla2sany.semantic.SemanticNode;
 
 import java.util.ArrayList;
+import java.util.List;
 
 public abstract class AbstractHasFollowers extends TLAType {
 
-	public ArrayList<Object> followers;
+	public List<Object> followers;
 
 	public AbstractHasFollowers(int t) {
 		super(t);
 		followers = new ArrayList<>();
 	}
 
-	public ArrayList<Object> getFollowers() {
+	public List<Object> getFollowers() {
 		return followers;
 	}
 
@@ -26,7 +27,6 @@ public abstract class AbstractHasFollowers extends TLAType {
 			}
 			followers.add(o);
 		}
-
 	}
 
 	public void deleteFollower(Object o) {
@@ -69,7 +69,6 @@ public abstract class AbstractHasFollowers extends TLAType {
 				if (pair.getSecond() == this) {
 					pair.setSecond(newType);
 				}
-
 			} else if (follower instanceof FunctionType) {
 				((FunctionType) follower).update(this, newType);
 			} else if (follower instanceof StructType) {
@@ -79,8 +78,7 @@ public abstract class AbstractHasFollowers extends TLAType {
 			} else if (follower instanceof TupleOrFunction) {
 				((TupleOrFunction) follower).setNewType(this, newType);
 			} else {
-				throw new RuntimeException("Unknown follower type: "
-					+ follower.getClass());
+				throw new RuntimeException("Unknown follower type: " + follower.getClass());
 			}
 		});
 	}
diff --git a/src/main/java/de/tla2b/types/AbstractSymbol.java b/src/main/java/de/tla2b/types/AbstractSymbol.java
index 8b9e3bfadeb6859ac147c664bc2d66513c273863..027cb69cbbc6bce861a6a5efeb473052f61e7b82 100644
--- a/src/main/java/de/tla2b/types/AbstractSymbol.java
+++ b/src/main/java/de/tla2b/types/AbstractSymbol.java
@@ -12,7 +12,6 @@ public abstract class AbstractSymbol {
 		return type;
 	}
 
-
 	protected void setType(TLAType t) {
 		this.type = t;
 		if (type instanceof AbstractHasFollowers) {