CeTA: 1: error when switching from the TRS
tail(cons(X)) -> L
incr(nil) -> nil
incr(cons(X)) -> cons(s(X))
adx(nil) -> nil
adx(cons(X)) -> incr(cons(X))
nats -> adx(zeros)
zeros -> cons(0)
head(cons(X)) -> X

to the initial DP problem
dependency pairs: 
nats# -> zeros#
nats# -> adx#(zeros)
adx#(cons(X)) -> incr#(cons(X))

rewrite system:
tail(cons(X)) -> L
incr(nil) -> nil
incr(cons(X)) -> cons(s(X))
adx(nil) -> nil
adx(cons(X)) -> incr(cons(X))
nats -> adx(zeros)
zeros -> cons(0)
head(cons(X)) -> X

the DP-transformation is not applied correctly.
the TRS is not well-formed
the variable L occurs only in the right-hand side of rule tail(cons(X)) -> L