diff --git a/src/main/java/_4/_1/Function.java b/src/main/java/_4/_1/Function.java
index 0483344..29c5ea4 100644
--- a/src/main/java/_4/_1/Function.java
+++ b/src/main/java/_4/_1/Function.java
@@ -2,22 +2,47 @@ package _4._1;
 
 public abstract class Function {
 
-	protected Function predecessor;
+	/**
+	 * For functions f and g,
+	 * g is the inner function of f in f(g(x))
+	 */
+	protected Function inner;
 
 	public Function() {
-		this.predecessor = null;
+		this.inner = null;
 	}
 
-	public Function(Function predecessor) {
-		this.predecessor = predecessor;
+	public Function(Function inner) {
+		this.inner = inner;
 	}
 
+	/**
+	 * <b>Note</b>: This method should probably not be overridden.
+	 * <p>
+	 * Computes the value of this (nested) function for x.
+	 * <p>
+	 * If this function is f and it's inner function is g,
+	 * then compute(x) returns f(g(x))
+	 *
+	 * @see #apply(double)
+	 */
 	public double calculate(double x) {
-		if(this.predecessor == null) {
+		if(this.inner == null) {
 			return this.apply(x);
 		}
-		return this.predecessor.calculate(x);
+		return this.inner.calculate(x);
 	}
 
+	/**
+	 * Computes the value of this function for x
+	 * <p>
+	 * If this function is f and it's inner function is g,
+	 * then apply(x) returns f(x)
+	 */
+	/*
+	 * protected to allow the this method to manipulate state
+	 * and still allow the developer to make assumptions about the state.
+	 * In most cases the implementation can be public.
+	 */
 	protected abstract double apply(double x);
 }
diff --git a/src/main/java/_4/_1/SineFunction.java b/src/main/java/_4/_1/SineFunction.java
index c2d6ace..cd49efb 100644
--- a/src/main/java/_4/_1/SineFunction.java
+++ b/src/main/java/_4/_1/SineFunction.java
@@ -5,8 +5,8 @@ public class SineFunction extends Function {
 		super();
 	}
 
-	public SineFunction(Function predecessor) {
-		super(predecessor);
+	public SineFunction(Function inner) {
+		super(inner);
 	}
 
 	@Override
diff --git a/src/main/java/_4/_1/SquareFunction.java b/src/main/java/_4/_1/SquareFunction.java
index f07e58b..e27adfa 100644
--- a/src/main/java/_4/_1/SquareFunction.java
+++ b/src/main/java/_4/_1/SquareFunction.java
@@ -5,12 +5,12 @@ public class SquareFunction extends Function {
 		super();
 	}
 
-	public SquareFunction(Function predecessor) {
-		super(predecessor);
+	public SquareFunction(Function inner) {
+		super(inner);
 	}
 
 	@Override
-	protected double apply(double x) {
+	public double apply(double x) {
 		return x * x;
 	}
 }