domain propagation

Dear all,

I need to enforce a constraint so that the domain of some of its variables
are not reduced during (domain) propagation. So far I've been using the
get_bounds/3 predicate to achieve this, as you can see in the following
example.

%+++ Example
   [eclipse 1] lib(ic).
   [eclipse 2] X #:: 0..1, get_bounds(X,B,T),
              (Y #:: 0..3, X + Y #< 4, indomain(Y),
               get_bounds(X,B1,T1), B1#=B, T1#=T).

   Y = 0
   X = X{[0, 1]}
   B1 = 0
   B = 0
   T1 = 1
   T = 1
   Yes (0.00s cpu, solution 1, maybe more) ? ;

   [eclipse 3]: X #:: 0..3, get_bounds(X,B,T), (Y #:: 0..1, X #= Y,
   get_bounds(X,B1,T1), B1 #= B, T1 #= T).

   No (0.00s cpu)
%+++

However, this is more of a trick than a general approach... Something
better could be achieved by having in ic/fd a version of

   #::(?Var,++Domain, ?Bool)

that returns Bool = 1 if and only if Domain is unchanged.

Any thought on this?

Thanks,
Piero