removeSubList( a, b ) {

		if ( a.prev === null ) {

			this.head = b.next;

		} else {

			a.prev.next = b.next;

		}

		if ( b.next === null ) {

			this.tail = a.prev;

		} else {

			b.next.prev = a.prev;

		}

		return this;

	}
Removes a sublist of vertices from the linked list.

@private
@param {VertexNode} a - The head of the sublist.
@param {VertexNode} b - The tail of the sublist.
@return {VertexList} A reference to this vertex list.