Spacer engine for HORN logic

The algorithms implemented in the engine are described in the following papers

Anvesh Komuravelli, Nikolaj Bjørner, Arie Gurfinkel, Kenneth L. McMillan:
Compositional Verification of Procedural Programs using Horn Clauses over Integers and Arrays. FMCAD 2015: 89-96

Nikolaj Bjørner, Arie Gurfinkel:
Property Directed Polyhedral Abstraction. VMCAI 2015: 263-281

Anvesh Komuravelli, Arie Gurfinkel, Sagar Chaki:
SMT-Based Model Checking for Recursive Programs. CAV 2014: 17-34

src/muz/spacer/spacer_proof_utils.h

@@ -0,0 +1,43 @@
+/*++
+Copyright (c) 2017 Arie Gurfinkel
+
+Module Name:
+
+    spacer_proof_utils.cpp
+
+Abstract:
+    Utilities to traverse and manipulate proofs
+
+Author:
+    Bernhard Gleiss
+    Arie Gurfinkel
+
+Revision History:
+
+--*/
+
+#ifndef _SPACER_PROOF_UTILS_H_
+#define _SPACER_PROOF_UTILS_H_
+#include "ast.h"
+
+namespace spacer {
+/*
+ * iterator, which traverses the proof in depth-first post-order.
+ */
+class ProofIteratorPostOrder {
+public:
+    ProofIteratorPostOrder(proof* refutation, ast_manager& manager);
+    bool hasNext();
+    proof* next();
+
+private:
+    ptr_vector<proof> m_todo;
+    ast_mark m_visited; // the proof nodes we have already visited
+
+    ast_manager& m;
+};
+
+
+void reduce_hypotheses(proof_ref &pr);
+}
+#endif