code: def check_declared(self, node):
          
  
          for ident in node.undeclared_identifiers():
              if ident != 'context' and\
                      ident not in self.declared.union(self.locally_declared):
                  self.undeclared.add(ident)
          for ident in node.declared_identifiers():
              self.locally_declared.add(ident)
docs: update the state of this Identifiers with the undeclared
              and declared identifiers of the given node.