How to listen for STRG + UP / STRG + DOWN the Rx way

gistfile1.txt

var keys = {
    UP: 38,
    DOWN: 40,
    CTRL: 17
}

var selectKeyCode = function(event){ return event.keyCode; };

var selectDown = function(){ return "down";};

var selectUp = function() { return "up" };

var areBothKeysDown = function(x, y) { return x === "down" && y === "down" };

var matchesKey = function(key){
    return function(x){
        return x === key;
    };
};

var observableKeyDowns = $(window).toObservable('keydown').Select(selectKeyCode);
var observableKeyUps = $(window).toObservable('keyup').Select(selectKeyCode);
            
var observableCtrlKeyDowns = observableKeyDowns.Where(matchesKey(keys['CTRL'])).Select(selectDown);                                    
var observableCtrlKeyUps = observableKeyUps.Where(matchesKey(keys['CTRL'])).Select(selectUp);                                    
var observableCtrlKeyState = Rx.Observable.Merge([observableCtrlKeyDowns, observableCtrlKeyUps])
                                    
var observableUpKeyDowns = observableKeyDowns.Where(matchesKey(keys['UP'])).Select(selectDown);                                    
var observableUpKeyUps = observableKeyUps.Where(matchesKey(keys['UP'])).Select(selectUp);                                    
var observableUpKeyState = Rx.Observable.Merge([observableUpKeyDowns, observableUpKeyUps]);
        
var observableDownKeyDowns = observableKeyDowns.Where(matchesKey(keys['DOWN'])).Select(selectDown);                                    
var observableDownKeyUps = observableKeyUps.Where(matchesKey(keys['DOWN'])).Select(selectUp);                                    
var observableDownKeyState = Rx.Observable.Merge([observableDownKeyDowns, observableDownKeyUps]);        

var observableCtrlAndUp = observableCtrlKeyState
                            .CombineLatest(observableUpKeyState, areBothKeysDown)
                            .Where(function(x){ return x === true;})
                            .Select(function(){ return "CtrlAndUp"; });
                            
var observableCtrlAndDown = observableCtrlKeyState
                            .CombineLatest(observableDownKeyState, areBothKeysDown)
                            .Where(function(x){ return x === true;})
                            .Select(function(){ return "CtrlAndDown"; });                            

var observableShortcuts = Rx.Observable.Merge([observableCtrlAndUp, observableCtrlAndDown]);

observableShortcuts.Subscribe(function(shortcut) { console.log(shortcut); });