[SMTCOMP] About the QF_IDL "n-queens" problms

[Roberto Sebastiani]

Dear colleagues,

Let me raise one more point, about "n-queens" problems in 
the QF_IDL benchmark suite. 
(I apologize for doing it only now, but we noticed this fact
only recently.)

297 out of 893 total benchmarks in QF_IDL  are "n-queens".
It seems to us they are all "pigeonhole-style" problems:

1. { x_i != x_j }_{ij}
2. { x_i=value_{i_1} | x_i=value_{i_2} | ... | x_i=value_{i_K} }_i

which are encoded into QF_IDL as

1.1. { x_i != x_j }_{ij}
2.1. { {i_1}  <= x_i-zero <= i_K }_i

("zero" being one variable representing zero).

Thus, they are FULLY-COMBINATORIAL CSP PROBLEMS disguised as 
SMT(QF_IDL) problems, and have hardly anything to do with QF_IDL.
In fact, no  arithmetical property should be exploited to solve 
these problems.
(Notice, e.g., that the actual values of the constants 
value_{i_j}'s are irrelevant: the only relevant fact is weather 
they are pairwise equal or different. Thus. "-" and ">=" have no 
effective mathematical meaning here.)

We believe this is against the spirit of SMT-COMP.
Moreover, these are the kind of problems which may push people 
to customize "ad hoc" solutions for the competition.

Thus, we believe these problems should be dropped from the list.

Roberto


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Prof. ROBERTO SEBASTIANI
Dip. Informatica e Telecomunicazioni
Fac. Scienze M.F.N., Universita` di Trento    Tel: +39 0461 881514
Via Sommarive 14, I-38050, Trento, Italy      Fax: +39 0461 882093
roberto.sebastiani at dit.unitn.it     http://www.dit.unitn.it/~rseba
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