diff --git a/10 generics/src/index.ts b/10 generics/src/index.ts
index 1c02e23..ef703c9 100644
--- a/10 generics/src/index.ts	
+++ b/10 generics/src/index.ts	
@@ -1,8 +1,8 @@
 /** A FIFO (First In First Out) collection */
 class Queue<T> {
-  data = [];
+  public data:T[] = [];
   push(item: T) { this.data.push(item); }
-  pop(): T { return this.data.shift(); }
+  pop(): T { return this.data.shift()! ; } // ! signifies that it can't be undefined
 }
 
 const queue = new Queue<number>();
@@ -10,4 +10,4 @@ queue.push(123);
 queue.push(456);
 
 console.log(queue.pop().toPrecision(1));
-console.log(queue.pop().toPrecision(1));
\ No newline at end of file
+console.log(queue.pop().toPrecision(1));
diff --git a/27 narrowing/src/index.ts b/27 narrowing/src/index.ts
index 96dc0b7..272cd5c 100644
--- a/27 narrowing/src/index.ts	
+++ b/27 narrowing/src/index.ts	
@@ -9,7 +9,7 @@ type Rectangle = {
 
 type Shape = Square | Rectangle;
 
-function area(shape: Shape) {
+function area(shape: Shape): void|number {
   if ('size' in shape) {
     return shape.size * shape.size;
   }
@@ -19,4 +19,4 @@ function area(shape: Shape) {
 }
 
 area({ size: 2 });             // 4
-area({ width: 2, height: 3 }); // 6
\ No newline at end of file
+area({ width: 2, height: 3 }); // 6