lessElementsltlessElt0lessEltniflelengthlnlelengthtoListtnltniftruebltnliffalsetrueltntiffalsefalseltnlessEltsnlengthnil0lengthconsnlslengthltoListleafniltoListnodet1nt2appendtoListt1consntoListt2appendnill2l2appendconsnl1l2consnappendl1l2lesn0falsele0mtruelesnsmlenmacad