add initial stubs for model reconstruction trail

src/ast/simplifiers/model_reconstruction_trail.cpp

@@ -0,0 +1,43 @@
+/*++
+Copyright (c) 2022 Microsoft Corporation
+
+Module Name:
+
+    model_reconstruction_trail.cpp
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2022-11-3.
+    
+--*/
+
+
+#include "ast/simplifiers/model_reconstruction_trail.h"
+#include "ast/converters/generic_model_converter.h"
+
+
+void model_reconstruction_trail::replay(dependent_expr const& d, vector<dependent_expr>& added) {
+    // accumulate a set of dependent exprs, updating m_trail to exclude loose 
+    // substitutions that use variables from the dependent expressions.
+    ast_mark free_vars;
+    auto [f, dep] = d;
+    for (expr* t : subterms::all(expr_ref(f, m))) 
+        free_vars.mark(t);
+    
+    NOT_IMPLEMENTED_YET();
+}
+
+/**
+ * retrieve the current model converter corresponding to chaining substitutions from the trail.
+ */
+model_converter_ref model_reconstruction_trail::get_model_converter() {
+    model_converter_ref mc = alloc(generic_model_converter, m, "dependent-expr-model");
+    // walk the trail from the back.
+    // add substitutions from the back to the generic model converter
+    // after they have been normalized using a global replace that replaces 
+    // substituted variables by their terms.
+    NOT_IMPLEMENTED_YET();
+    return mc;
+
+}
+