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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _process_value(self, d, from_where):
 """ Pre-process an AST for insertion into unicorn. :param d: the AST :param from_where: the ID of the memory region it comes from ('mem' or 'reg') :returns: the value to be inserted into Unicorn, or None """

        if len(d.annotations):
            l.debug("Blocking annotated AST.")
            return None
        elif not d.symbolic:
            return d
        else:
            l.debug("Processing AST with variables %s.", d.variables)

        dd = self._symbolic_passthrough(d)

        if not dd.symbolic:
            if d.symbolic:
                l.debug("... concretized")
            return dd
        elif from_where == 'reg' and options.UNICORN_SYM_REGS_SUPPORT in self.state.options:
            l.debug("... allowing symbolic register")
            return dd
        else:
            l.debug("... denied")
            return None