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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 inference_rule.h
+/// @brief Abstract interface for pluggable inference rules.
+///
+/// Each inference rule (resolution, factoring, paramodulation, etc.)
+/// is a self-contained object that the Prover can selectively load.
+/// This prevents search space explosion by only enabling rules relevant
+/// to the problem at hand.
+
+#include "atp/core/clause.h"
+#include "atp/core/clause_store.h"
+#include "atp/core/term_bank.h"
+
+#include <string_view>
+#include <vector>
+
+namespace atp {
+
+/// Abstract base class for all inference rules.
+/// The Prover invokes only the rules present in its active calculus.
+class InferenceRuleBase {
+  public:
+    virtual ~InferenceRuleBase() = default;
+
+    /// Human-readable name for logging and proof output.
+    [[nodiscard]] virtual std::string_view name() const = 0;
+
+    /// Is this a generating rule (produces new clauses) or simplifying rule
+    /// (rewrites/deletes existing clauses)?
+    enum class Kind : uint8_t { kGenerating, kSimplifying };
+    [[nodiscard]] virtual Kind kind() const = 0;
+};
+
+/// Generating inference rule: given a "given clause" and the set of processed
+/// clauses, produce new clauses.
+class GeneratingRule : public InferenceRuleBase {
+  public:
+    [[nodiscard]] Kind kind() const final { return Kind::kGenerating; }
+
+    /// Generate new clauses from the given clause against all processed clauses.
+    /// @param given     The selected clause from the Unprocessed queue.
+    /// @param processed All previously processed clauses (accessed via store).
+    /// @param bank      The global term bank.
+    /// @return Newly generated clauses (not yet added to the store).
+    [[nodiscard]] virtual std::vector<Clause> generate(const Clause& given,
+                                                       const std::vector<ClauseId>& processed,
+                                                       const ClauseStore& store,
+                                                       TermBank& bank) const = 0;
+};
+
+/// Simplifying inference rule: rewrite or delete a clause in-place.
+class SimplifyingRule : public InferenceRuleBase {
+  public:
+    [[nodiscard]] Kind kind() const final { return Kind::kSimplifying; }
+
+    /// Attempt to simplify a clause. Returns true if the clause was modified.
+    /// If the clause should be deleted entirely, clear its literals.
+    virtual bool simplify(Clause& clause, const ClauseStore& store, TermBank& bank) const = 0;
+};
+
+}  // namespace atp