fst 0 Z nil fst s X cons Y Z cons Y fst X Z from X cons X from s X add 0 X X add s X Y s add X Y len nil 0 len cons X Z s len Z fst 2 0 0 nil 0 s 1 cons 2 from 1 add 2 len 1 INNERMOST ./TRS/nontermin/CSR/Ex2_Luc03b.trs