NEWS

   1 This file contains a summary of important user-visible changes.
   2
   3 Changes since 1.8
   4 =================
   5
   6 New Features:
   7
   8 * New unsat-core production modes based on the new proof infrastructure
   9   (`--unsat-cores-mode=sat-proof`) and on the solving-under-assumption feature
  10   of Minisat (`--unsat-cores-mode=assumptions`). The mode based on SAT
  11   assumptions + preprocessing proofs is the new default.
  12 * A new parametric theory of sequences whose syntax is compatible with the
  13   syntax for sequences used by Z3.
  14 * Arrays: Added support for an `eqrange` predicate. `(eqrange a b i j)` is true
  15   if arrays `a` and `b` are equal on all indices within indices `i` and `j`.
  16 * Support for an integer operator `(_ iand n)` that returns the bitwise `and`
  17   of two integers, seen as integers modulo n.
  18
  19 Improvements:
  20 * New API: Added functions to retrieve the heap/nil term when using separation
  21   logic.
  22
  23 Changes:
  24 * SyGuS: Removed support for SyGuS-IF 1.0.
  25 * Removed Java and Python bindings for the legacy API
  26 * Interactive shell: the GPL-licensed Readline library has been replaced the
  27   BSD-licensed Editline. Compiling with `--best` now enables Editline, instead
  28   of Readline. Without selecting optional GPL components, Editline-enabled CVC4
  29   builds will be BSD licensed.
  30 * The semantics for division and remainder operators in the CVC language now
  31   correspond to SMT-LIB 2.6 semantics (i.e. a division by zero or a zero
  32   modulus results in a constant value, instead of an uninterpreted one).
  33   Similarly, when no language is set, the API semantics now correspond to the
  34   SMT-LIB 2.6 semantics.
  35 * The `competition` build type includes the dependencies used for SMT-COMP by
  36   default. Note that this makes this build type produce GPL-licensed binaries.
  37 * Bit-vector operator bvxnor was previously mistakenly marked as
  38   left-assoicative in SMT-LIB. This has recently been corrected in SMT-LIB. We
  39   now restrict bvxnor to only allow two operands in order to avoid confusion
  40   about the semantics, since the behavior of n-ary operands to bvxnor is now
  41   undefined in SMT-LIB.
  42 * SMT-LIB output for `get-model` command now conforms with the standard,
  43   and does *not* begin with the keyword `model`. The output
  44   is the same as before, only with this word removed from the beginning.
  45 * Building with Python 2 is now deprecated.
  46
  47
  48 Changes since 1.7
  49 =================
  50
  51 New Features:
  52 * New C++ and Python API: CVC4 has a new, more streamlined API. We plan to
  53   make CVC4 1.8 the last version that ships with the legacy API.
  54 * Strings: Full support of the new SMT-LIB standard for the theory of strings,
  55   including:
  56   * Support for `str.replace_re`, `str.replace_re_all`, `str.is_digit`,
  57     `str.from_code`, `re.diff`, and `re.comp`
  58   * Support for new operator names (e.g. `str.in_re` instead of `str.in.re`),
  59     new escape sequences. The new syntax is enabled by default for smt2 files.
  60 * Support for syntax-guided synthesis (SyGuS) problems in the new API. C++
  61   examples of the SyGuS API can be found in `./examples/api/sygus_*.cpp`.
  62 * Support for higher-order constraints. This includes treating function sorts
  63   (constructible by `->`) as first-class sorts and handling partially applied
  64   function symbols. Support for higher-order constraints can be enabled by
  65   the option `--uf-ho`.
  66 * Support for set comprehension binders `comprehension`.
  67 * Eager bit-blasting: Support for SAT solver Kissat.
  68
  69 Improvements:
  70 * API: Function definitions can now be requested to be global. If the `global`
  71   parameter is set to true, they persist after popping the user context.
  72 * Java/Python bindings: The bindings now allow users to catch exceptions
  73 * Arithmetic: Performance improvements
  74   * Linear solver: New lemmas inspired by unit-cube tests
  75   * Non-linear solver: Expanded set of axioms
  76 * Ackermannization: The Ackermannization preprocessing pass now supports
  77   uninterpreted sorts and as a result all QF_UFBV problems are supported in
  78   combination with eager bit blasting.
  79
  80 Changes:
  81 * CVC language: Models printed in the CVC language now include an explicit end
  82   marker to facilitate the communication over pipes with CVC4.
  83 * API change: `SmtEngine::query()` has been renamed to
  84   `SmtEngine::checkEntailed()` and `Result::Validity` has been renamed to
  85   `Result::Entailment` along with corresponding changes to the enum values.
  86 * Java API change: The name of CVC4's package is now `edu.stanford.CVC4`
  87   instead of `edu.nyu.acsys.CVC4`.
  88 * The default output language is changed from CVC to SMT-LIB 2.6. The
  89   default output language is used when the problem language cannot be
  90   easily inferred (for example when CVC4 is used from the API).
  91 * Printing of BV constants: previously CVC4 would print BV constant
  92   values as indexed symbols by default and in binary notation with the
  93   option --bv-print-consts-in-binary. To be SMT-LIB compliant the
  94   default behavior is now to print BV constant values in binary
  95   notation and as indexed symbols with the new option
  96   --bv-print-consts-as-indexed-symbols. The option
  97   --bv-print-consts-in-binary has been removed.
  98 * Updated to SyGuS language version 2.0 by default. This is the last release
  99   that will support the SyGuS language version 1.0 (`--lang=sygus1`). A
 100   script is provided to convert version 1.0 files to version 2.0, see
 101   `./contrib/sygus-v1-to-v2.sh`.
 102 * Support for user-provided rewrite rule quantifiers have been removed.
 103 * Support for certain option aliases have been removed.
 104 * Support for parallel portfolio builds has been removed.
 105
 106 Changes since 1.6
 107 =================
 108
 109 New Features:
 110 * Proofs:
 111   * Support for bit-vector proofs with eager bitblasting (older versions only
 112     supported proofs with lazy bitblasting).
 113 * Strings:
 114   * Support for `str.replaceall` operator.
 115   * New option `--re-elim` to reduce regular expressions to extended string
 116     operators, resulting in better performance on regular expression benchmarks
 117     (enabled by default).
 118 * SyGuS:
 119   * Support for abduction (`--sygus-abduct`). Given a formula, this option uses
 120     CVC4's SyGuS solver to find a sufficient condition such that the
 121     conjunction of the condition and the formula is unsatisfiable.
 122   * Support for two new term enumerator strategies: variable agnostic
 123     (`--sygus-active-gen=var-agnostic`) and fast (`--sygus-active-gen=enum`).
 124     By default, CVC4 tries to choose the best term enumerator strategy
 125     automatically based on the input (`--sygus-active-gen=auto`).
 126   * Support for streaming solutions of increasingly smaller size when using the
 127     PBE solver (`--sygus-stream --sygus-pbe`). After the first solution is found
 128     and printed, the solver will continue to look for new solutions and print
 129     those, if any, that are smaller than previously printed solutions.
 130   * Support for unification-based techniques in non-separable specifications
 131     (`--sygus-unif`). For solving invariant problems a dedicate mode
 132     (`--sygus-unif-boolean-heuristic-dt`) is available that builds candidate
 133     solutions using heuristic decision tree learning.
 134
 135 Improvements:
 136 * Strings:
 137   * Significantly better performance on string benchmarks over the core theory
 138     and those with extended string functions like substring, contains, and
 139     replace.
 140
 141 Changes:
 142 * API change: Expr::iffExpr() is renamed to Expr::eqExpr() to reflect its
 143               actual behavior.
 144 * Compiling the language bindings now requires SWIG 3 instead of SWIG 2.
 145 * The CVC3 compatibility layer has been removed.
 146 * The build system now uses CMake instead of Autotools. Please refer to
 147   [INSTALL.md](https://github.com/CVC4/CVC4/blob/master/INSTALL.md) for
 148   up-to-date instructions on how to build CVC4.
 149
 150 Changes since 1.5
 151 =================
 152
 153 New Features:
 154 * A new theory of floating points.
 155 * Novel approach for solving quantified bit-vectors (BV).
 156 * Eager bit-blasting: Support for SAT solver CaDiCaL.
 157 * A new Gaussian Elimination preprocessing pass for the theory of bit-vectors.
 158 * Support for transcendental functions (sin, cos, exp). In SMT2 input, this
 159   can be enabled by adding T to the logic (e.g., QF_NRAT).
 160 * Support for new operators in strings, including string inequality (str.<=)
 161   and string code (str.code).
 162 * Support for automated rewrite rule generation from sygus (*.sy) inputs using
 163   syntax-guided enumeration (option --sygus-rr).
 164
 165 Improvements:
 166 * Incremental unsat core support.
 167 * Further development of rewrite rules for the theory of strings and regular
 168   expressions.
 169 * Many optimizations for syntax-guided synthesis, including improved symmetry
 170   breaking for enumerative search and specialized algorithms for
 171   programming-by-examples conjectures.
 172
 173 Changes:
 174 * Eager bit-blasting: Removed support for SAT solver CryptoMinisat 4, added
 175   support for CryptoMinisat 5.
 176 * The LFSC proof checker now resides in its own repository on GitHub at
 177   https://github.com/CVC4/LFSC. It is not distributed with CVC4 anymore.
 178
 179 Changes since 1.4
 180 =================
 181
 182 * Improved heuristics for reasoning about non-linear arithmetic.
 183 * Native support for syntax-guided synthesis (sygus).
 184 * Support for many new heuristics for reasoning with quantifiers, including
 185   finite model finding.
 186 * Support for proofs for uninterpreted functions, arrays, bitvectors, and
 187   their combinations.
 188 * Performance improvements to existing theories.
 189 * A new theory of sets with cardinality and relations.
 190 * A new theory of strings.
 191 * Support for unsat cores.
 192 * Support for separation logic constraints.
 193 * Simplification mode "incremental" no longer supported.
 194 * Support for array constants in constraints.
 195 * Syntax for array models has changed in some language front-ends.
 196 * New input/output languages supported: "smt2.0" and "smtlib2.0" to
 197   force SMT-LIB v2.0; "smt2.5" and "smtlib2.5" to force SMT-LIB v2.5;
 198   "smt2.6" and "smtlib2.6" to force SMT-LIB v2.6;
 199   "smt", "smtlib", "smt2", and "smtlib2" all refer to the current standard
 200   version 2.6.  If an :smt-lib-version is set in the input, that overrides
 201   the command line.
 202 * Abstract values in SMT-LIB models are now ascribed types (with "as").
 203 * In SMT-LIB model output, real-sorted but integer-valued constants are
 204   now printed in accordance with the standard (e.g. "1.0").
 205
 206 Changes since 1.3
 207 =================
 208
 209 * CVC4 now supports libc++ in addition to libstdc++ (this especially
 210   helps on Mac OS Mavericks).
 211 * The LFSC proof checker has been incorporated into CVC4 sources.
 212 * Theory of finite sets, handling the MLSS fragment (singleton, union,
 213   intersection, set subtraction, membership and subset).
 214 * By default, CVC4 builds in "production" mode (optimized, with fewer
 215   internal checks on).  The common alternative is a "debug" build, which
 216   is much slower.  By default, CVC4 builds with no GPL'ed dependences.
 217   However, this is not the best-performing version; for that, you should
 218   configure with "--enable-gpl --best", which links against GPL'ed
 219   libraries that improve usability and performance.  For details on
 220   licensing and dependences, see the README file.
 221 * Small API adjustments to Datatypes to even out the API and make it
 222   function better in Java.
 223 * Timed statistics are now properly updated even on process abort.
 224 * Better automatic handling of output language setting when using CVC4
 225   via API.  Previously, the "automatic" language setting was sometimes
 226   (though not always) defaulting to the internal "AST" language; it
 227   should now (correctly) default to the same as the input language
 228   (if the input language is supported as an output language), or the
 229   "CVC4" native output language if no input language setting is applied.
 230 * The SmtEngine cannot be safely copied with the copy constructor.
 231   Previous versions inadvertently permitted clients to do this via the
 232   API.  This has been corrected, copy and assignment of the SmtEngine
 233   is no longer permitted.
 234
 235 Changes since 1.2
 236 =================
 237
 238 New features:
 239 * SMT-LIB-compliant support for abs, to_real, to_int, is_int, which were
 240   previously missing
 241 * New bv2nat/int2bv operators for bitvector/integer inter-compatibility.
 242 * Support in linear logics for /, div, and mod by constants (with the
 243   --rewrite-divk command line option).
 244 * Parsing support for TPTP's TFF and TFA formats.
 245 * A new theory of strings: word (dis-)equations, length constraints,
 246   regular expressions.
 247 * Increased compliance to SMT-LIBv2, numerous bugs and usability issues
 248   resolved.
 249 * New :command-verbosity SMT option to silence success and error messages
 250   on a per-command basis, and API changes to Command infrastructure to
 251   support this.
 252
 253 Behavioral changes:
 254 * It is no longer permitted to request model or proof generation if there's
 255   been an intervening push/pop.
 256 * User-defined symbols (define-funs) are no longer reported in the output
 257   of get-model commands.
 258 * Exit codes are now more standard for UNIX command-line tools.  Exit code
 259   zero means no error---but the result could be sat, unsat, or unknown---and
 260   nonzero means error.
 261
 262 API changes:
 263 * Expr::substitute() now capable of substituting operators (e.g.,
 264   function symbols under an APPLY_UF)
 265 * Numerous improvements to the Java language bindings
 266
 267 Changes since 1.1
 268 =================
 269
 270 * Real arithmetic now has three simplex solvers for exact precision linear
 271   arithmetic: the classical dual solver and two new solvers based on
 272   techniques for minimizing the sum of infeasibilities. GLPK can now be used
 273   as a heuristic backup to the exact precision solvers.  GLPK must be enabled
 274   at configure time. See --help for more information on enabling these solvers.
 275 * added support for "bit0" and "bit1" bitvector constants in SMT-LIB v1.2
 276 * support for theory "alternates": new ability to prototype new decision
 277   procedures that are selectable at runtime
 278 * various bugfixes
 279
 280 Changes since 1.0
 281 =================
 282
 283 * bit-vector solver now has a specialized decision procedure for unsigned bit-
 284   vector inequalities
 285 * numerous important bug fixes, performance improvements, and usability
 286   improvements
 287 * support for multiline input in interactive mode
 288 * Win32-building support via mingw
 289 * SMT-LIB get-model output now is easier to machine-parse: contains (model...)
 290 * user patterns for quantifier instantiation are now supported in the
 291   SMT-LIBv1.2 parser
 292 * --finite-model-find was incomplete when using --incremental, now fixed
 293 * the E-matching procedure is slightly improved
 294 * Boolean terms are now supported in datatypes
 295 * tuple and record support have been added to the compatibility library
 296 * driver verbosity change: for printing all commands as they're executed, you
 297   now need verbosity level >= 3 (e.g., -vvv) instead of level 1 (-v).  This
 298   allows tracing the solver's activities (with -v and -vv) without having too
 299   much output.
 300 * to make CVC4 quieter in abnormal (e.g., "warning" conditions), you can
 301   use -q.  Previously, this would silence all output (including "sat" or
 302   "unsat") as well.  Now, single -q silences messages and warnings, and
 303   double -qq silences all output (except on exception or signal).