Typescript: generic interface, interface functions and class type parameters

I am trying to implement a generic discrete interval encoding tree with typescript. Generic here means I want to allow interval endpoints to be arbitrary classes that extends a simple interface specifying discrete linear orders which enforces the existence of two method members next and lessThan. Because I want to type the methods I assume I need a generic interface (all the code can be found in this jsfiddle):

interface DiscreteLinearOrder<T> {
    next = () => T;
    lessThan = (y: T) => Boolean;
}

Then I instantiated this with number (ok, it is not discrete, but think of it as integers ;-)

class DLOnumber implements DiscreteLinearOrder<number> {
    private value: number;
    constructor(x: number) { this.value = x; }
    next = () => { return(this.value + 1); };
    lessThan = (y: number) => { return(this.value < y); };
    getValue = () => { return(this.value.toString()); }
}

Up to here it worked, and running things like

const bar = new DLOnumber(5);

worked out.

Having this I planed to provide a class DLOinterval that takes two parameters, one extending the discrete linear order interface:

class DLOinterval<T, U extends DiscreteLinearOrder<T>> {
    private start: U;
    private end: U;
    private data: any;
    constructor(s: U, e: U, d: any) {
        this.start = s;
        this.end   = e;
        this.data  = d;
    }
}

But here the troubles are starting: I cannot define a type alias and use it:

type NumberInterval = DLOinterval<number, DLOnumber>;
const ggg = new NumberInterval(new DLOnumber(3),new DLOnumber(5),null)

neither can I instantiate it directly:

const aaa = new DLOinterval<number, DLOnumber>(new DLOnumber(3),new DLOnumber(5),null)

What am I missing here?