Fix bug reported by Philippe Suter, see RELEASE_NOTES

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

RELEASE_NOTES

@@ -30,6 +30,21 @@ Version 4.3.2
   
 - Fixed problem in the pretty printer. It was not introducing quotes for attribute names such as |foo:10|.
 
+- Fixed bug when using assumptions (Thanks to Philippe Suter)
+  Consider the following example:
+      (assert F)
+      (check-sat a)
+      (check-sat)
+  If 'F' is unstatisfiable independently of the assumption 'a', and 
+  the inconsistenty can be detected by just performing propagation,
+  Then, version <= 4.3.1 may return
+      unsat
+      sat
+  instead of
+      unsat
+      unsat
+  We say may because 'F' may have other unsatisfiable cores.
+
 Version 4.3.1
 =============
 

src/smt/smt_context.cpp

@@ -2854,7 +2854,12 @@ namespace smt {
         m_bool_var2assumption.reset();
         m_unsat_core.reset();
         if (num_assumptions > 0) {
-            propagate(); // we must give a chance to the theories to propagate before we create a new scope...
+            // We must give a chance to the theories to propagate before we create a new scope...
+            propagate(); 
+            // Internal backtracking scopes (created with push_scope()) must only be created when we are
+            // in a consistent context.
+            if (inconsistent())
+                return; 
             push_scope();
             for (unsigned i = 0; i < num_assumptions; i++) {
                 expr * curr_assumption = assumptions[i];
@@ -3987,3 +3992,8 @@ namespace smt {
 
 };
 
+#ifdef Z3DEBUG
+void pp(smt::context & c) {
+    c.display(std::cout);
+}
+#endif