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+/*
+ * richard-atp-engine: A saturation-based automated theorem prover for first-order logic.
+ * Copyright (C) 2026 Richard Qin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/// @file clausifier.h
+/// @brief Converts FOL formulas to Clause Normal Form (CNF).
+///
+/// Clausifier is a stateful object because:
+///   1. Skolem function counter must be shared across all formulas in a problem
+///      (otherwise different formulas generate conflicting Skolem names).
+///   2. Variable renaming counter must be shared for the same reason.
+///
+/// Pipeline: eliminate ↔/→  →  NNF  →  Skolemize  →  distribute ∨ over ∧  →  flatten.
+
+#include "atp/core/clause.h"
+#include "atp/core/symbol_table.h"
+#include "atp/core/term_bank.h"
+#include "atp/normalize/formula.h"
+
+#include <vector>
+
+namespace atp {
+
+/// Stateful clausifier. Create one per proof problem.
+///
+/// Usage:
+///   Clausifier clausifier(bank, symbols);
+///   auto clauses1 = clausifier.clausify(formula1);
+///   auto clauses2 = clausifier.clausify(formula2);
+///   // Skolem IDs are unique across both calls.
+class Clausifier {
+  public:
+    Clausifier(TermBank& bank, SymbolTable& symbols);
+
+    /// Convert a single formula to CNF clauses.
+    /// Skolem functions generated here are globally unique (counter persists).
+    [[nodiscard]] std::vector<Clause> clausify(const Formula& formula);
+
+    /// Negate a formula: wraps it in ¬(...)
+    /// Used to negate the conjecture before clausification.
+    [[nodiscard]] static std::unique_ptr<Formula> negate(std::unique_ptr<Formula> formula);
+
+    /// Number of Skolem functions generated so far.
+    [[nodiscard]] uint32_t skolemCount() const { return next_skolem_id_; }
+
+  private:
+    TermBank& bank_;
+    SymbolTable& symbols_;
+    uint32_t next_skolem_id_ = 0;
+    uint32_t next_var_id_ = 0;  ///< For variable standardization apart
+};
+
+}  // namespace atp