diff --git a/Lab4/Applicable.java b/Lab4/Applicable.java
index c764ebb..31b8efb 100644
--- a/Lab4/Applicable.java
+++ b/Lab4/Applicable.java
@@ -5,9 +5,10 @@
  * Contains a single abstract method apply.
  * CS2030S Lab 4
  * AY22/23 Semester 1
+ * 
  * @author Yadunand Prem (10B)
  */
 
 interface Applicable<T> {
-  <R> Applicable<R> apply(Probably<Immutator<R, T>> probablyImmutator);
+  <R> Applicable<R> apply(Probably<? extends Immutator<? extends R, ? super T>> probablyImmutator);
 }
diff --git a/Lab4/Immutatorable.java b/Lab4/Immutatorable.java
index b9d277c..396890d 100644
--- a/Lab4/Immutatorable.java
+++ b/Lab4/Immutatorable.java
@@ -9,5 +9,5 @@
  */
 
 interface Immutatorable<T> {
-  public <R> Immutatorable<R> transform(Immutator<R, T> immutator);
+  public <R> Immutatorable<R> transform(Immutator<? extends R, ? super T> immutator);
 }
diff --git a/Lab4/Probably.java b/Lab4/Probably.java
index 628c9d4..0d402eb 100644
--- a/Lab4/Probably.java
+++ b/Lab4/Probably.java
@@ -41,7 +41,7 @@ class Probably<T> implements Actionable<T>, Immutatorable<T>, Applicable<T> {
    * Unless the value is null, then nothing is
    * given again.
    *
-   * @param <T> type T
+   * @param <T>   type T
    *
    * @param value Probably this is the value
    *              unless it is null then we say
@@ -105,21 +105,18 @@ class Probably<T> implements Actionable<T>, Immutatorable<T>, Applicable<T> {
     action.call(this.value);
   }
 
-  public Probably<T> check(IsModEq eq) {
+  public Probably<T> check(Immutator<Boolean, ? super T> eq) {
     if (this.value == null) {
       return none();
     }
-    if (this.value instanceof Integer) {
-      Integer val = (Integer) this.value;
-      if (eq.invoke(val)) {
-        return this;
-      }
+    if (eq.invoke(this.value)) {
+      return this;
     }
     return none();
   }
 
   @Override
-  public <R> Probably<R> transform(Immutator<R, T> immutator) {
+  public <R> Probably<R> transform(Immutator<? extends R, ? super T> immutator) {
     if (this.value == null) {
       return none();
     }
@@ -127,9 +124,9 @@ class Probably<T> implements Actionable<T>, Immutatorable<T>, Applicable<T> {
   }
 
   @Override
-  public <R> Probably<R> apply(Probably<Immutator<R, T>> probablyImmutator) {
-    if (this.value != null && probablyImmutator.value != null) {
-      return just(probablyImmutator.value.invoke(this.value));
+  public <R> Probably<R> apply(Probably<? extends Immutator<? extends R, ? super T>> probablyImmutator) {
+    if (probablyImmutator.value != null) {
+      return this.transform(probablyImmutator.value);
     }
     return none();
   }