1 Release Notes for CVC4 1.5, July 2017
5 If you run CVC4 without arguments, you will find yourself in an interactive
6 CVC4 session, which expects commands in CVC4's native language (the so-called
7 "presentation" language). To use SMT-LIB, use the "--lang smt" option on the
8 command line. For stricter adherence to the standard, use "--smtlib-strict"
9 (see below regarding SMT-LIB compliance).
11 When a filename is given on the command line, the file's extension determines
12 the language parser that's used (e.g., file.smt is SMT-LIB 1.2, file.smt2
13 is SMT-LIB 2.6, and file.cvc is the presentation language). To override
14 this, you can use the --lang option.
18 The CVC family of systems relies on Type Correctness Conditions (TCCs) when
19 mixing two types that have a compatible base type. TCCs, and the checking of
20 such, are not supported by CVC4 1.5. This is an issue when mixing integers and
21 reals. A function defined only on integers can be applied to REAL (as INT is a
22 subtype of REAL), and CVC4 will not complain. It is up to the user to ensure
23 that the REAL expression must be an integer. If the REAL expression is not
24 an integer and is used where an INT is expected, CVC4 may produce strange
35 % f : (INT) -> INT = LAMBDA(x1:INT) : 0;
37 This kind of problem can be identified by checking TCCs. Though CVC4 does not
38 (yet) support TCCs, CVC3 can be used to produce TCCs for this input (with the
39 +dump-tcc option). The TCC can then be checked by CVC4 or another solver.
40 (CVC3 can also check TCCs at the same time it creates them, with +tcc.)
42 ** Changes in CVC's Presentation Language
44 The native language of all solvers in the CVC family, referred to as the
45 "presentation language," has undergone some revisions for CVC4. The
46 most notable is that CVC4 does _not_ add counterexample assertions to
47 the current assertion set after a SAT/INVALID result. For example:
50 ASSERT x = 1 OR x = 2;
51 ASSERT y = 1 OR y = 2;
60 Here, CVC4 responds "invalid" to the second and third queries, because
61 each has a counterexample (x=2 is a counterexample to the first, and
62 x=1 is a counterexample to the second). However, CVC3 will respond
63 with "valid" to one of these two, as the first query (the CHECKSAT)
64 had the side-effect of locking CVC3 into one of the two cases; the
65 later queries are effectively querying the counterexample that was
66 found by the first. CVC4 removes this side-effect of the CHECKSAT and
69 CVC4 supports rational literals (of type REAL) in decimal; CVC3 did not
72 CVC4 does not have support for predicate subtypes, although these are
73 planned for future releases.
77 Every effort has been made to make CVC4 compliant with the SMT-LIB 2.6
78 standard (http://smtlib.org/). However, when parsing SMT-LIB input,
79 certain default settings don't match what is stated in the official
80 standard. To make CVC4 adhere more strictly to the standard, use the
81 "--smtlib-strict" command-line option. Even with this setting, CVC4 is
82 somewhat lenient; some non-conforming input may still be parsed and
85 For the latest news on SMT-LIB compliance, please check:
87 http://cvc4.cs.stanford.edu/wiki/SMT-LIB_Compliance
91 Statistics can be dumped on exit (both normal and abnormal exits) with
92 the --stats command line option.
94 ** Time and resource limits
96 CVC4 can be made to self-timeout after a given number of milliseconds.
97 Use the --tlimit command line option to limit the entire run of
98 CVC4, or use --tlimit-per to limit each individual query separately.
99 Occasionally, you may encounter a problem for which --tlimit does not work very
100 well. If you suspect this might be the case, please report it as a bug. You
101 can also use "-vv" (double verbosity) to see what CVC4 is doing.
103 Time-limited runs are not deterministic; two consecutive runs with the
104 same time limit might produce different results (i.e., one may time out
105 and respond with "unknown", while the other completes and provides an
106 answer). To ensure that results are reproducible, use --rlimit or
107 --rlimit-per. These options take a "resource count" (presently, based on
108 the number of SAT conflicts) that limits the search time. A word of
109 caution, though: there is no guarantee that runs of different versions of
110 CVC4 or of different builds of CVC4 (e.g., two CVC4 binaries with different
111 features enabled, or for different architectures) will interpret the resource
112 count in the same manner.
114 CVC4 does not presently have a way to limit its memory use; you may opt
115 to run it from a shell after using "ulimit" to limit the size of the
120 CVC4 1.5 has support for proofs when using uninterpreted functions, arrays,
121 bitvectors, or their combinations, and proofs are enabled by default.
122 (Run the configure script with --disable-proof to disable proofs). Proofs
123 are exported in LFSC format.
125 ** Nonlinear arithmetic
127 CVC4 1.5 has a state-of-the-art linear arithmetic solver as well as some
128 heuristic support for non-linear arithmetic.
132 If enabled at configure-time (./configure --with-portfolio), a second
133 CVC4 binary will be produced ("pcvc4"). This binary has support for
134 running multiple instances of CVC4 in different threads. Use --threads=N
135 to specify the number of threads, and use --thread0="options for thread 0"
136 --thread1="options for thread 1", etc., to specify a configuration for the
137 threads. Lemmas are *not* shared between the threads by default; to adjust
138 this, use the --filter-lemma-length=N option to share lemmas of N literals
139 (or smaller). (Some lemmas are ineligible for sharing because they include
140 literals that are "local" to one thread.)
142 Currently, the portfolio **does not work** with the theory of inductive
143 datatypes. This limitation will be addressed in a future release.
147 CVC4 and its predecessors have an active user base. You might want to
148 subscribe to the mailing list (http://cvc4.stanford.edu/#Technical_Support)
149 and post a question there.
151 ** Reporting bugs and making feature requests
153 CVC4 is under active development. Should you find a bug in CVC4's
154 documentation, behavior, API, or SMT-LIB compliance, or if you have
155 a feature request, please let us know on our bugtracker at
157 https://github.com/CVC4/CVC4/issues
159 or send an email to cvc-bugs@cs.stanford.edu.