CeTA: 1: error when switching from the TRS
tail(cons(X)) -> XS
zeros -> cons(0)

to the initial DP problem
dependency pairs: 

rewrite system:
tail(cons(X)) -> XS
zeros -> cons(0)

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