///
module Rx {
export interface Observable {
/**
* Returns the element at a specified index in a sequence or default value if not found.
* @param {Number} index The zero-based index of the element to retrieve.
* @param {Any} [defaultValue] The default value to use if elementAt does not find a value.
* @returns {Observable} An observable sequence that produces the element at the specified position in the source sequence.
*/
elementAt(index: number): Observable;
}
}
(function () {
var o : Rx.Observable;
o = o.elementAt(5);
});