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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 has_mixture_channel(val: Any) -> bool: """Returns whether the value has a mixture channel representation. In contrast to `has_mixture` this method falls back to checking whether the value has a unitary representation via `has_channel`. Returns: If `val` has a `_has_mixture_` method and its result is not NotImplemented, that result is returned. Otherwise, if `val` has a `_has_unitary_` method and its results is not NotImplemented, that result is returned. Otherwise, if the value has a `_mixture_` method that is not a non-default value, True is returned. Returns False if none of these functions. """

    mixture_getter = getattr(val, '_has_mixture_', None)
    result = NotImplemented if mixture_getter is None else mixture_getter()
    if result is not NotImplemented:
        return result

    result = has_unitary(val)
    if result is not NotImplemented and result:
        return result

    # No _has_mixture_ or _has_unitary_ function, use _mixture_ instead.
    return mixture_channel(val, None) is not None