impure predicates

[Henk Vandecasteele]

Dear,

I have a number of impure predicates. These predicates have only 
input-arguments. The code works fine, except for one detail:
these predicates have several solutions, the system ought to backrack 
over these solution. 
When these predicates are given a dummy output-
argument ( representing a state of the world) then it works.

I tought this was a typical application where the impure-declaration
would help me out. A small experiment seems to proved me wrong. 
(experiment done with rotd-1998-09-25)

So, should the mercury-system backtrack over impure
predicates which have only input-arguments?

Regards,

Henk