  We describe how to device-independently generate a set of quantum states for
which unambiguous state discrimination is not possible. First, we derive a
formula that a certain non-signaling black box must satisfy. Then, we describe
how to generate a set of quantum states. Devices for generating states and
possible measurements on the states can be put into a black box. Because this
black box is non-signaling, it satisfies the formula. Using the formula, we
prove that unambiguous state discrimination is not possible for the generated
states. Because we did not consider internal mechanisms but only outcomes, our
argument is valid for any (imperfect) devices.
