/**
 * Interface for a stack of primitive doubles.
 */
interface DStack {
    /** 
     * Test whether this stack is empty.
     * @return <code>true</code> if stack is empty, <code>false</code> if not
     */
    boolean isEmpty();

    /**
     * Push a new item on top of this stack.
     * @param d value to be pushed
     */
    void push(double d);

    /**
     * Delete the value that is on top of this stack.
     * @return the value that was deleted
     * @throws EmptyStackException if stack is empty
     */
    double pop();

    /**
     * Return the value that is on top of this stack without deleting it.
     * @throws EmptyStackException if stack is empty
     */
    double top();
}