chain(+Zs,
+Relation)Zs form a chain with respect to Relation. Zs
is a list of finite domain variables that are a chain with respect to
the partial order
Relation, in the order they appear in the list. Relation
must be #=,
#=<, #>=, #< or #>.
For example:
?- chain([X,Y,Z], #>=).
X#>=Y,
Y#>=Z.