Polysat: conflict resolution wip (#5529)

* conflict_core doesn't need gc() anymore

* update comments, ensure_bvar for new constraints

* Make sure constraints can only be created through constraint_manager

* fix constraint::display if no boolean variable is assigned

* Move clause into separate file

* Add conflict_core binary resolution

* conflict_core additions

* reactivate conflict resolution outer loop

* wip

* seems commented includes break CI build

src/math/polysat/variable_elimination.h

@@ -0,0 +1,52 @@
+/*++
+Copyright (c) 2021 Microsoft Corporation
+
+Module Name:
+
+    Polysat variable elimination
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-19
+    Jakob Rath 2021-04-6
+
+--*/
+#pragma once
+#include "math/polysat/conflict_core.h"
+
+namespace polysat {
+
+    class variable_elimination_engine {
+    public:
+        virtual ~variable_elimination_engine() {}
+        virtual bool perform(pvar v, conflict_core& core) = 0;
+    };
+
+    // discovers when a variable has already been removed... (special case of ve_reduction?)
+    class ve_trivial final : public variable_elimination_engine {
+    public:
+        bool perform(pvar v, conflict_core& core) override { NOT_IMPLEMENTED_YET(); return false; }
+    };
+
+    // ve by core reduction: try core reduction on all constraints that contain the variable to be eliminated.
+    // if we cannot eliminate all such constraints, then should we keep all of them instead of eliminating only some? since they might still be useful for saturation.
+    class ve_reduction final : public variable_elimination_engine {
+    public:
+        bool perform(pvar v, conflict_core& core) override { NOT_IMPLEMENTED_YET(); return false; }
+    };
+
+    class ve_forbidden_intervals final : public variable_elimination_engine {
+    public:
+        bool perform(pvar v, conflict_core& core) override { NOT_IMPLEMENTED_YET(); return false; }
+    };
+
+    class variable_elimination final {
+        scoped_ptr_vector<variable_elimination_engine> ve_engines;
+
+    public:
+        variable_elimination() {}
+
+        /// Try to eliminate the variable v from the given core
+        bool perform(pvar v, conflict_core& core) { NOT_IMPLEMENTED_YET(); return false; }
+    };
+}