frozen/2
frozen(
+Var,
-Goal)
Goal is unified with the conjunction of goals blocked on Var.
If some goal is blocked on the variable Var, or Var has
attributes that can be interpreted as a goal (see lib-atts),
then that goal is unified with Goal. If no goals are blocked,
Goal is unified with the atom true
. If more than one
goal is blocked, a conjunction is unified with Goal.
type_error