Fixing commonSuperType and canBeAssignedTo methods for ReferenceType

lisa/lisa-sdk/src/main/java/it/unive/lisa/type/ReferenceType.java

@@ -30,13 +30,18 @@ public ReferenceType(
 	@Override
 	public boolean canBeAssignedTo(
 			Type other) {
-		return other instanceof PointerType || other.isUntyped();
+		return other instanceof ReferenceType && getInnerType().canBeAssignedTo(other.asReferenceType().getInnerType()) || other.isUntyped();
 	}
 
 	@Override
 	public Type commonSupertype(
 			Type other) {
-		return equals(other) ? this : Untyped.INSTANCE;
+		if (equals(other))
+			return this;
+		else if (other instanceof ReferenceType)
+			return new ReferenceType(getInnerType().commonSupertype(other.asReferenceType().getInnerType()));
+
+		return Untyped.INSTANCE;
 	}
 
 	@Override