cleanup nla_solver

Signed-off-by: Lev <levnach@hotmail.com>

src/util/lp/factorization.h

@@ -0,0 +1,40 @@
+
+  /*++
+  Copyright (c) 2017 Microsoft Corporation
+
+  Module Name:
+
+  <name>
+
+  Abstract:
+
+  <abstract>
+
+  Author:
+  Nikolaj Bjorner (nbjorner)
+  Lev Nachmanson (levnach)
+
+  Revision History:
+
+
+  --*/
+namespace nla {
+
+class factorization {
+    svector<lpvar>         m_vars;
+    rational               m_sign;
+    std::function<void (expl_set&)> m_explain;
+public:
+    void explain(expl_set& s) const { m_explain(s); }
+    bool is_empty() const { return m_vars.empty(); }
+    svector<lpvar> & vars() { return m_vars; }
+    const svector<lpvar> & vars() const { return m_vars; }
+    rational const& sign() const { return m_sign; }
+    rational& sign() { return m_sign; } // the setter
+    unsigned operator[](unsigned k) const { return m_vars[k]; }
+    size_t size() const { return m_vars.size(); }
+    const lpvar* begin() const { return m_vars.begin(); }
+    const lpvar* end() const { return m_vars.end(); }
+    factorization(std::function<void (expl_set&)> explain) : m_explain(explain) {}
+};
+}