Array.prototype.isHeavySlope = function() {
    if (this.length == 0) return true;
    var pre, sub;
    for each (var n in this) {
        if (pre == undefined) {
            sub = pre = n;
        } else {
            sub -= n;
            if (pre <= n || sub <= 0) return false;
            pre = n;
        }
    }
    return true;
}