add module for handling axioms for powers

src/math/lp/nla_powers.h

@@ -0,0 +1,29 @@
+/*++
+Copyright (c) 2017 Microsoft Corporation
+
+Module Name:
+
+  nla_powers.h
+
+Author:
+  Lev Nachmanson (levnach)
+  Nikolaj Bjorner (nbjorner)
+
+Description:
+  Refines bounds on powers.
+  
+--*/
+
+#include "math/lp/nla_types.h"
+
+namespace nla {
+    
+    class core;
+    
+    class powers {
+        core& m_core;
+    public:
+        powers(core& c):m_core(c) {}
+        lbool check(lpvar r, lpvar x, lpvar y, vector<lemma>&);
+    };
+}