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Notes on limitations of the solving libraries and other implementation details.

CLP(FD)
=====================
* Solvers using CLP(FD) will return error if there are constraint variables 
  that still have an infinite/unspecified domain (i.e., inf..sup) after all 
  constraints have been asserted.
  Consider using cspvar/3 for all constraint variables.
  A ramification of this is that the clearbox mode (--cmodels-feedback) may
  not work.


SWI-Prolog
=====================
* clp(fd) returns an error if there are constraint variables whose upper bound
  is sup or whose lower bound is inf after all constraints have been asserted.
  For example:
    cspvar(x).
    required(x #>= 3).
  will cause an error. Note that its translation to SWI-Prolog is equivalent
  to:
    :- use_module(library(clpfd)).
    X #>= 3, labeling([],[X]).
  Consider using cspvar/3 for all constraint variables.
  A ramification of this is that the clearbox mode (--cmodels-feedback) may
  not work.
