if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function(elt /*, from*/) {
        var len = this.length;
        var from = Number(arguments[1]) || 0;

        from = (from < 0) ? Math.ceil(from) : Math.floor(from);
        if (from < 0) { from += len; }

        for (; from < len; from++) {
            if (from in this && this[from] === elt)
                return from;
        }
        return -1;
    };
}

Array.prototype.remove = function(s) {
    var i = this.indexOf(s);
    if (i != -1) this.splice(i, 1);
}

Array.prototype.include = function(s) {
    var i = this.indexOf(s);
    if (i == -1) this.push(s);
}