hi i need help with this

ok so i'm using flash to program obviously and i am trying to initialize a collision for a roof it says Collision has not been declared.

i have

    import flash.display.MovieClip;

    import flash.events.KeyboardEvent;

    import flash.ui.Keyboard;

    import flash.events.Event;

    public class Main_Ninja extends MovieClip

    {

        var vx:int;

        var vy:int;

        var score:uint;

        var collisionHasOccurred:Boolean;

        var playerHasMoney:Boolean;

i am trying to initialize

Collision.block(player, roof);

but when i try to initialize that it gets stuck in an infinite loop for this

if (player.hitTestObject(enemy))

            {

                enemy.gotoAndStop(2);

                health.meter.width--;

                if (! collisionHasOccurred)

                {

                    score++;

                    messageDisplay.text = String(score);

                    collisionHasOccurred = true;

                }

            }

            else

            {

                enemy.gotoAndStop(1);

                collisionHasOccurred = false;

            }

please help me if you can.