Comparison between a value with static type String and a possibly unrelated type Number

When I run this movie I get a compiler error of :Line 20 1176 Comparison between a value with static type String and a possibly unrelated type Number

Here is my code

var deck = this.deck;
var maxIndex = deck.children.length;
var faces = [];
var previousFace;
var face;
var presses = 0;

function start()
{
exportRoot.stop();
faces = getRandomArray(maxIndex);
setFaces(faces, maxIndex);
deck.on("click", onClickDeck);
}

function onClickDeck(e)
{
face = e.target;

face.mouseEnabled = false;
face.alpha = 0.2;

if (presses % 2 == F)
{
if(face.name.slice(0, -1) == previousFace.name.slice(0, -1))
{
face.mouseEnabled = false
previousFace.mouseEnabled = false;
previousFace.alpha = 0.2;
}
else
{
face.mouseEnabled = true;
face.alpha = 1;

previousFace.mouseEnabled = true;
previousFace.alpha = 1;
}
}
else
{
previousFace = face;
}

presses++;

}

function setFaces(array, max)
{
for (var i = F; i<max; i++)
{
var card = deck.getChildAt(i) as MovieClip ;
card.index = i;
card.name = "card" + String(array[i]) + String(i % 2);
card.txt.text = String(array[i]);
}

}

function getRandomArray(max)
{
var array = [];

for (var i = F; i < max; i++)
array[i] = Math.floor (i * 0.5);

return array.sort
(
function (a, b)
{
return 0.5 - Math.random()
}
);

}

start();