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sorts inhabited by default? #22

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kanigsson opened this issue Apr 1, 2015 · 3 comments
Closed

sorts inhabited by default? #22

kanigsson opened this issue Apr 1, 2015 · 3 comments

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@kanigsson
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Hi all,

on the VC below Z3 answers "unsat" although one could argue that it's not ... the critical question is whether sorts are always inhabited or not. Clearly Z3 assumes that yes, but the SMTlib standard doesn't say anything about this as far as I can see. And other SMT-solvers (I tried CVC4 and Alt-ergo) don't exploit this.

So what is your opinion on this? Thanks in advance,

Johannes

================ VC below ===================

(declare-sort t 0)

(define-fun in_range ((x Int)) Bool (and (<= 1 x) (<= x 0)))

(declare-fun to_rep (t) Int)

;; range_axiom
(assert (forall ((x t)) (in_range (to_rep x))))

(check-sat)
@LeventErkok
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I'll just point out that in traditional many-sorted logic sorts are typically assumed to be non-empty. So, I'd posit that SMTLib probably follows the same tradition. Also see here: http://en.wikipedia.org/wiki/First-order_logic#Empty_domains

It would be good to be explicit about it in the SMTLib doc, of course.

@NikolajBjorner
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Yes, this is standard that sorts are inhabited and Z3 assumes/uses this throughout.

@kanigsson
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Makes sense, the issue can be closed. Thanks for your answers.

@itszor itszor mentioned this issue Jun 1, 2015
Closed
NikolajBjorner added a commit to NikolajBjorner/z3 that referenced this issue Jul 31, 2016
@NikolajBjorner @levnach
fix bound bug (Z3Prover#22)
df21c95 
* fix bound bug

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

* fix bounds check

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
@chadbrewbaker chadbrewbaker mentioned this issue Nov 13, 2016
Closed
@qingkaishi qingkaishi mentioned this issue Nov 21, 2016
Closed
@ngilmore-grammatech ngilmore-grammatech mentioned this issue Feb 2, 2018
Closed
@levnach levnach mentioned this issue Nov 28, 2018
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@5hadowblad3 5hadowblad3 mentioned this issue Mar 16, 2020
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@levnach levnach mentioned this issue Mar 18, 2020
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@rainoftime rainoftime mentioned this issue Apr 6, 2020
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@hgvk94 hgvk94 mentioned this issue Apr 24, 2020
Open
mtzguido added a commit to mtzguido/z3 that referenced this issue Jun 23, 2023
@mtzguido
bool_rewriter: fix possible segfault when disabling rewriter.sort_dis…
ccd828e 
…junctions

After introducing the rewriter.sort_disjunctions option, I noticed a
segfault in a Z3 run that was working fine for me.

I traced the difference to a slight discrepancy between the first patch
I submitted and the one we ended up merging: my first version would skip
sorting the disjuncts in mk_nflat_core, but still return BR_DONE, while
the patch in master returns BR_FAILED instead.

This patch fixes the problem for me, and it makes slightly more sense
to me to return a BR_DONE since, if `s` is true, some disjunct (e.g. a
`false` or a repeat) might have been simplified away. However I don't
fully understand this code.

.. and I can't say I understand why the segfault happens. Perhaps that
is a separate issue?

This is the file to reproduce:
 https://gist.github.com/mtzguido/b7360c74d3d2e42d89f1bd9149ad26f6

Here's a stack trace of the failure, mk_nflat_or_core is not involved.
```
 (gdb) where
 #0  0x0000555555b98497 in smt::context::get_lit_assignment(unsigned int) const ()
 Z3Prover#1  0x0000555555b984cb in smt::context::get_assignment(sat::literal) const ()
 Z3Prover#2  0x0000555555b98504 in smt::context::get_assignment(unsigned int) const ()
 Z3Prover#3  0x0000555555ca83b8 in smt::context::get_assignment_core(expr*) const ()
 Z3Prover#4  0x0000555555c9af5a in smt::context::get_assignment(expr*) const ()
 Z3Prover#5  0x0000555555d7bd1d in (anonymous namespace)::has_child_assigned_to(smt::context&, app*, lbool, expr*&, unsigned int) ()
 Z3Prover#6  0x0000555555d7c413 in (anonymous namespace)::rel_case_split_queue::next_case_split_core(ptr_vector<expr>&, unsigned int&, unsigned int&, lbool&) ()
 Z3Prover#7  0x0000555555d7c589 in (anonymous namespace)::rel_case_split_queue::next_case_split(unsigned int&, lbool&) ()
 Z3Prover#8  0x0000555555c9c1b7 in smt::context::decide() ()
 Z3Prover#9  0x0000555555ca39fd in smt::context::bounded_search() ()
 Z3Prover#10 0x0000555555ca30c2 in smt::context::search() ()
 Z3Prover#11 0x0000555555ca273d in smt::context::check(unsigned int, expr* const*, bool) ()
 Z3Prover#12 0x0000555555cb166a in smt::kernel::check(unsigned int, expr* const*) ()
 Z3Prover#13 0x0000555555cb9695 in (anonymous namespace)::smt_solver::check_sat_core2(unsigned int, expr* const*) ()
 Z3Prover#14 0x00005555560dc0c6 in solver_na2as::check_sat_core(unsigned int, expr* const*) ()
 Z3Prover#15 0x00005555560d73f3 in combined_solver::check_sat_core(unsigned int, expr* const*) ()
 Z3Prover#16 0x00005555560d34e3 in solver::check_sat(unsigned int, expr* const*) ()
 Z3Prover#17 0x0000555556097b26 in cmd_context::check_sat(unsigned int, expr* const*) ()
 Z3Prover#18 0x0000555556082ff0 in smt2::parser::parse_check_sat() ()
 Z3Prover#19 0x0000555556084dc0 in smt2::parser::parse_cmd() ()
 Z3Prover#20 0x00005555560861b6 in smt2::parser::operator()() ()
 Z3Prover#21 0x00005555560757e6 in parse_smt2_commands(cmd_context&, std::basic_istream<char, std::char_traits<char> >&, bool, params_ref const&, char const*) ()
 Z3Prover#22 0x00005555555e8f68 in read_smtlib2_commands(char const*) ()
 Z3Prover#23 0x00005555555ee6f6 in main ()
 (gdb)
```
mtzguido added a commit to mtzguido/z3 that referenced this issue Jun 23, 2023
@mtzguido
bool_rewriter: fix possible segfault when disabling rewriter.sort_dis…
c9c5f1e 
…junctions

After introducing the rewriter.sort_disjunctions option (Z3Prover#6774), I
noticed a segfault in a Z3 run that was working fine for me before the
PR.

I traced the difference to a slight discrepancy between the first patch
I submitted and the one we ended up merging: my first version would skip
sorting the disjuncts in mk_nflat_core, but still return BR_DONE, while
the patch in master returns BR_FAILED instead.

This patch fixes that problem, and it makes slightly more sense to me to
return a BR_DONE since, if `s` is true, some disjunct (e.g. a `false`
or a repeat) might have been simplified away. However I don't fully
understand this code.

... and I can't say I understand why the segfault happens. Perhaps that
is a separate issue?

This is the file to reproduce:
 https://gist.github.com/mtzguido/b7360c74d3d2e42d89f1bd9149ad26f6

Here's a stack trace of the failure, mk_nflat_or_core is not involved.
```
 (gdb) where
 #0  0x0000555555b98497 in smt::context::get_lit_assignment(unsigned int) const ()
 Z3Prover#1  0x0000555555b984cb in smt::context::get_assignment(sat::literal) const ()
 Z3Prover#2  0x0000555555b98504 in smt::context::get_assignment(unsigned int) const ()
 Z3Prover#3  0x0000555555ca83b8 in smt::context::get_assignment_core(expr*) const ()
 Z3Prover#4  0x0000555555c9af5a in smt::context::get_assignment(expr*) const ()
 Z3Prover#5  0x0000555555d7bd1d in (anonymous namespace)::has_child_assigned_to(smt::context&, app*, lbool, expr*&, unsigned int) ()
 Z3Prover#6  0x0000555555d7c413 in (anonymous namespace)::rel_case_split_queue::next_case_split_core(ptr_vector<expr>&, unsigned int&, unsigned int&, lbool&) ()
 Z3Prover#7  0x0000555555d7c589 in (anonymous namespace)::rel_case_split_queue::next_case_split(unsigned int&, lbool&) ()
 Z3Prover#8  0x0000555555c9c1b7 in smt::context::decide() ()
 Z3Prover#9  0x0000555555ca39fd in smt::context::bounded_search() ()
 Z3Prover#10 0x0000555555ca30c2 in smt::context::search() ()
 Z3Prover#11 0x0000555555ca273d in smt::context::check(unsigned int, expr* const*, bool) ()
 Z3Prover#12 0x0000555555cb166a in smt::kernel::check(unsigned int, expr* const*) ()
 Z3Prover#13 0x0000555555cb9695 in (anonymous namespace)::smt_solver::check_sat_core2(unsigned int, expr* const*) ()
 Z3Prover#14 0x00005555560dc0c6 in solver_na2as::check_sat_core(unsigned int, expr* const*) ()
 Z3Prover#15 0x00005555560d73f3 in combined_solver::check_sat_core(unsigned int, expr* const*) ()
 Z3Prover#16 0x00005555560d34e3 in solver::check_sat(unsigned int, expr* const*) ()
 Z3Prover#17 0x0000555556097b26 in cmd_context::check_sat(unsigned int, expr* const*) ()
 Z3Prover#18 0x0000555556082ff0 in smt2::parser::parse_check_sat() ()
 Z3Prover#19 0x0000555556084dc0 in smt2::parser::parse_cmd() ()
 Z3Prover#20 0x00005555560861b6 in smt2::parser::operator()() ()
 Z3Prover#21 0x00005555560757e6 in parse_smt2_commands(cmd_context&, std::basic_istream<char, std::char_traits<char> >&, bool, params_ref const&, char const*) ()
 Z3Prover#22 0x00005555555e8f68 in read_smtlib2_commands(char const*) ()
 Z3Prover#23 0x00005555555ee6f6 in main ()
 (gdb)
```
NikolajBjorner pushed a commit that referenced this issue Jun 23, 2023
@mtzguido
bool_rewriter: fix possible segfault when disabling rewriter.sort_dis…
7c380fd 
…junctions (#6779)

After introducing the rewriter.sort_disjunctions option (#6774), I
noticed a segfault in a Z3 run that was working fine for me before the
PR.

I traced the difference to a slight discrepancy between the first patch
I submitted and the one we ended up merging: my first version would skip
sorting the disjuncts in mk_nflat_core, but still return BR_DONE, while
the patch in master returns BR_FAILED instead.

This patch fixes that problem, and it makes slightly more sense to me to
return a BR_DONE since, if `s` is true, some disjunct (e.g. a `false`
or a repeat) might have been simplified away. However I don't fully
understand this code.

... and I can't say I understand why the segfault happens. Perhaps that
is a separate issue?

This is the file to reproduce:
 https://gist.github.com/mtzguido/b7360c74d3d2e42d89f1bd9149ad26f6

Here's a stack trace of the failure, mk_nflat_or_core is not involved.
```
 (gdb) where
 #0  0x0000555555b98497 in smt::context::get_lit_assignment(unsigned int) const ()
 #1  0x0000555555b984cb in smt::context::get_assignment(sat::literal) const ()
 #2  0x0000555555b98504 in smt::context::get_assignment(unsigned int) const ()
 #3  0x0000555555ca83b8 in smt::context::get_assignment_core(expr*) const ()
 #4  0x0000555555c9af5a in smt::context::get_assignment(expr*) const ()
 #5  0x0000555555d7bd1d in (anonymous namespace)::has_child_assigned_to(smt::context&, app*, lbool, expr*&, unsigned int) ()
 #6  0x0000555555d7c413 in (anonymous namespace)::rel_case_split_queue::next_case_split_core(ptr_vector<expr>&, unsigned int&, unsigned int&, lbool&) ()
 #7  0x0000555555d7c589 in (anonymous namespace)::rel_case_split_queue::next_case_split(unsigned int&, lbool&) ()
 #8  0x0000555555c9c1b7 in smt::context::decide() ()
 #9  0x0000555555ca39fd in smt::context::bounded_search() ()
 #10 0x0000555555ca30c2 in smt::context::search() ()
 #11 0x0000555555ca273d in smt::context::check(unsigned int, expr* const*, bool) ()
 #12 0x0000555555cb166a in smt::kernel::check(unsigned int, expr* const*) ()
 #13 0x0000555555cb9695 in (anonymous namespace)::smt_solver::check_sat_core2(unsigned int, expr* const*) ()
 #14 0x00005555560dc0c6 in solver_na2as::check_sat_core(unsigned int, expr* const*) ()
 #15 0x00005555560d73f3 in combined_solver::check_sat_core(unsigned int, expr* const*) ()
 #16 0x00005555560d34e3 in solver::check_sat(unsigned int, expr* const*) ()
 #17 0x0000555556097b26 in cmd_context::check_sat(unsigned int, expr* const*) ()
 #18 0x0000555556082ff0 in smt2::parser::parse_check_sat() ()
 #19 0x0000555556084dc0 in smt2::parser::parse_cmd() ()
 #20 0x00005555560861b6 in smt2::parser::operator()() ()
 #21 0x00005555560757e6 in parse_smt2_commands(cmd_context&, std::basic_istream<char, std::char_traits<char> >&, bool, params_ref const&, char const*) ()
 #22 0x00005555555e8f68 in read_smtlib2_commands(char const*) ()
 #23 0x00005555555ee6f6 in main ()
 (gdb)
```
@rammohan02 rammohan02 mentioned this issue Feb 10, 2024
Closed
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3 participants
@kanigsson @LeventErkok @NikolajBjorner