VOIT

     Iteration Validity rule

     An Iteration is valid if and only if it satisfies the
     following conditions:

        1 The type of the Expression conforms to ITERABLE
          [T] (based on the Kernel Library class ITERABLE)
          for some type T. (By VHPR (5), this T is unique.)

        2 The Identifier does not have the same lower name
          as any feature of the enclosing class, or any
          formal argument or local variable of any
          enclosing feature or Inline_agent, or the
          Object-test Local of any enclosing Object_test,
          or the Identifier of any enclosing Iteration.