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TPTP frontend: enforce implicit universal quantification for free variables and add regression coverage (#9527)

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Discussion #9524 reported systematic TPTP result polarity errors
(notably `Unsatisfiable/Theorem` cases returned as `Satisfiable`) and
timeout-path instability in the frontend. The dominant issue was
semantic: free variables in FOF/CNF formulas were parsed as constants
instead of implicitly universally quantified variables.

- **Parser semantics: free variables now follow TPTP rules**
- In `/home/runner/work/z3/z3/src/cmd_context/tptp_frontend.cpp`, free
variables encountered while parsing an annotated formula are now
collected in formula scope and wrapped with a top-level `forall`.
- This applies to both term and atomic-formula paths, so variable
occurrences are treated consistently.
- Explicitly bound quantifier variables continue to take precedence over
implicit ones.

- **Scoped implementation cleanup**
- Added scoped state for implicit-variable collection to avoid leaking
parser state across formulas.
- Kept variable binding order stable so quantifier construction is
deterministic.

- **Timeout-path robustness**
- Updated frontend exception catches to `const&` in the TPTP stream
entrypoint to make timeout/error handling behavior consistent with
thrown exception forms.

- **Regression tests**
- Extended `/home/runner/work/z3/z3/src/test/tptp.cpp` with focused
cases for:
    - FOF free-variable implicit universal quantification.
    - CNF free-variable implicit universal quantification.

```tptp
cnf(c1,axiom, p(X)).
cnf(c2,axiom, ~ p(a)).
```

This now maps to `forall X. p(X)` plus `~p(a)`, yielding `% SZS status
Unsatisfiable` as expected.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>
This commit is contained in:
Copilot 2026-05-13 13:19:14 -04:00 • committed by GitHub
parent 6b69c2c048
commit ce07160d64
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GPG key ID: B5690EEEBB952194
2 changed files with 59 additions and 2 deletions
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53
src/cmd_context/tptp_frontend.cpp
View file

@ -265,6 +265,11 @@ class tptp_parser {
func_decl_ref_vector m_pinned_decls; // prevents cached func_decls from being freed
std::unordered_map<std::string, std::pair<std::vector<sort*>, sort*>> m_typed_decls;
std::vector<std::unordered_map<std::string, app*>> m_bound;
struct implicit_var_scope {
std::unordered_map<std::string, app*> vars;
ptr_vector<app> order;
};
implicit_var_scope* m_implicit_scope = nullptr;
std::unordered_set<std::string> m_seen_files;
std::string m_input;
@ -454,6 +459,39 @@ class tptp_parser {
return false;
}
bool should_create_implicit_var(std::string const& n) const {
return is_var_name(n) && m_implicit_scope;
}
app* get_or_create_implicit_var(std::string const& n) {
if (!m_implicit_scope)
throw parse_error("unexpected parser state: missing implicit variable scope");
auto it = m_implicit_scope->vars.find(n);
if (it != m_implicit_scope->vars.end()) return it->second;
app* c = m.mk_const(symbol(n), m_univ);
m_implicit_scope->vars.emplace(n, c);
m_implicit_scope->order.push_back(c);
return c;
}
class scoped_implicit_vars {
tptp_parser& m_p;
implicit_var_scope* m_prev_scope;
public:
scoped_implicit_vars(tptp_parser& p, implicit_var_scope& scope):
m_p(p),
m_prev_scope(p.m_implicit_scope) {
m_p.m_implicit_scope = &scope;
}
scoped_implicit_vars(scoped_implicit_vars const&) = delete;
scoped_implicit_vars& operator=(scoped_implicit_vars const&) = delete;
scoped_implicit_vars(scoped_implicit_vars&&) = delete;
scoped_implicit_vars& operator=(scoped_implicit_vars&&) = delete;
~scoped_implicit_vars() {
m_p.m_implicit_scope = m_prev_scope;
}
};
expr_ref mk_quantifier(bool is_forall, ptr_vector<app> const& bound, expr_ref const& body) {
SASSERT(body);
if (bound.empty()) return body;
@ -607,6 +645,8 @@ class tptp_parser {
expr_ref b(m);
if (is_var_name(n) && find_bound(n, b))
return b;
if (should_create_implicit_var(n))
return expr_ref(get_or_create_implicit_var(n), m);
expr_ref_vector args(m);
if (accept(token_kind::lparen)) {
@ -823,6 +863,10 @@ class tptp_parser {
lhs = b;
has_lhs = true;
}
else if (should_create_implicit_var(n)) {
lhs = expr_ref(get_or_create_implicit_var(n), m);
has_lhs = true;
}
}
if (is(token_kind::equal_tok) || is(token_kind::neq_tok)) {
@ -1076,7 +1120,12 @@ class tptp_parser {
parse_type_decl_formula();
}
else {
implicit_var_scope implicit_scope;
scoped_implicit_vars scoped(*this, implicit_scope);
expr_ref f = parse_formula();
if (!implicit_scope.order.empty()) {
f = mk_quantifier(true, implicit_scope.order, f);
}
if (role == "conjecture") {
m_has_conjecture = true;
f = m.mk_not(f);
@ -1249,7 +1298,7 @@ static unsigned read_tptp_stream(std::istream& in, char const* current_file) {
std::cerr << "TPTP parse error: " << ex.what() << "\n";
return ERR_PARSER;
}
catch (z3_error& ex) {
catch (z3_error const& ex) {
if (ex.error_code() == ERR_TIMEOUT) {
std::cout << "% SZS status Timeout\n";
return 0;
@ -1257,7 +1306,7 @@ static unsigned read_tptp_stream(std::istream& in, char const* current_file) {
std::cerr << "TPTP frontend error: " << ex.what() << "\n";
return ERR_INTERNAL_FATAL;
}
catch (z3_exception& ex) {
catch (z3_exception const& ex) {
std::cerr << "TPTP frontend error: " << ex.what() << "\n";
return ERR_INTERNAL_FATAL;
}

8
src/test/tptp.cpp
View file

@ -65,6 +65,14 @@ fof(c1,conjecture, mortal(socrates)).)",
{"simple-sat",
R"(fof(a1,axiom, p(a)).)",
"% SZS status Satisfiable"},
{"fof-implicit-forall",
R"(fof(a1,axiom, p(X)).
fof(c1,conjecture, p(a)).)",
"% SZS status Theorem"},
{"cnf-implicit-forall",
R"(cnf(c1,axiom, p(X)).
cnf(c2,axiom, ~ p(a)).)",
"% SZS status Unsatisfiable"},
{"tff-negative-literal",
R"(tff(c1,conjecture, $less(-2,2)).)",
"% SZS status Theorem"},