Polysat: conflict explanation prototype (#5353)

* display constraint's extra info in one place

* Add stub for conflict explainer

* Add helper functions to check whether constraint is active at base level

* Add helper class tmp_assign

* Add clause_builder; it skips unnecessary literals during clause creation

* some fixes

* Use clause_builder for forbidden intervals

* remove old comments

* fixes/comments in solver

* print redundant clauses

* First pass at conflict_explainer

* remove unused model class

* Choose value for k

* also print min/max k

src/math/polysat/explain.h

@@ -0,0 +1,43 @@
+/*++
+Copyright (c) 2021 Microsoft Corporation
+
+Module Name:
+
+    Conflict explanation / resolution
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-19
+    Jakob Rath 2021-04-6
+
+--*/
+#pragma once
+#include "math/polysat/constraint.h"
+#include "math/polysat/interval.h"
+#include "math/polysat/solver.h"
+
+namespace polysat {
+
+    // TODO: later, we probably want to update this class incrementally (adding/removing constraints as we go back through the trail)
+    // TODO: indexing of constraints/clauses?
+    class conflict_explainer {
+        solver& m_solver;
+        constraints_and_clauses m_conflict;
+        pvar m_var = null_var;
+        ptr_vector<constraint> m_cjust_v;
+
+
+        clause_ref by_polynomial_superposition();
+
+        clause_ref by_ugt_x();
+        clause_ref by_ugt_y();
+        clause_ref by_ugt_z();
+
+        p_dependency_ref null_dep() const { return m_solver.mk_dep_ref(null_dependency); }
+        void push_omega_mul(clause_builder& clause, unsigned level, unsigned p, pdd const& x, pdd const& y);
+    public:
+        conflict_explainer(solver& s, constraints_and_clauses const& conflict);
+
+        clause_ref resolve(pvar v, ptr_vector<constraint> const& cjust_v);
+    };
+}