• Int is bound to a non-integer.
• Int is a negative integer.
• List is neither a list nor a partial list. This error condition includes cyclic lists.^{121ISO demands failure here. We think an error is more appropriate.}

This predicate fails if the tail of List is equivalent to Int (e.g., length(L,L)).^{122This is logically correct. An exception would be more appropriate, but to our best knowledge, current practice in Prolog does not describe a suitable candidate exception term.}