add outline for ule constraints, change bit to var constraints

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/math/polysat/var_constraint.h

@@ -0,0 +1,42 @@
+/*++
+Copyright (c) 2021 Microsoft Corporation
+
+Module Name:
+
+    polysat var_constraint
+
+Abstract:
+
+    Var constraints restrict viable values.
+
+    The main way var-constraints interact with the solver is to 
+    narrow m_viable during initialization. 
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2021-03-19
+    Jakob Rath 2021-04-6
+
+--*/
+#pragma once
+#include "math/dd/dd_bdd.h"
+#include "math/polysat/constraint.h"
+
+
+namespace polysat {
+
+    class var_constraint : public constraint {
+        pvar        m_var;
+        bdd         m_viable;
+    public:
+        var_constraint(unsigned lvl, pvar v, bdd const & b, p_dependency_ref& dep):
+            constraint(lvl, dep, ckind_t::bit_t), m_var(v), m_viable(b) {}
+        ~var_constraint() override {}
+        std::ostream& display(std::ostream& out) const override;
+        bool propagate(solver& s, pvar v) override;
+        constraint* resolve(solver& s, pvar v) override;
+        void narrow(solver& s) override;
+        bool is_always_false() override;
+        bool is_currently_false(solver& s) override;
+    };
+}