CeTA: 1: error when switching from the TRS
tail(cons(X)) -> XS
nats -> cons(0)
pairs -> cons(0)
odds -> incr(pairs)
incr(cons(X)) -> cons(s(X))
head(cons(X)) -> X

to the initial DP problem
dependency pairs: 
odds# -> incr#(pairs)
odds# -> pairs#

rewrite system:
tail(cons(X)) -> XS
nats -> cons(0)
pairs -> cons(0)
odds -> incr(pairs)
incr(cons(X)) -> cons(s(X))
head(cons(X)) -> X

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