 How can such cases be handled from a structuralist point of view? Is structuralism (of this kind) simply incoherent, as some of its critics charge? Or is it at least not applicable to non-rigid cases, which would limit its reach significantly? Several responses to the identity problem have been offered in the literature. One suggestion is to “rigidify” such structures by enlarging the vocabulary that is used, e.g., by adding the constant symbol ‘i’ for the complex numbers (either into the original language or into the language for the “setting” used in the background, cf. Halimi 2019). But this still seems problematic in the case of many indiscernibles, perhaps even uncountably many. Another suggestion is to treat identity as a primitive notion, as is arguably part of mathematical practice. But in that case too a number of questions remain (see Ladyman 2005, Button 2006, Leitgeb &amp; Ladyman 2008, Shapiro 2008, Ketland 2011, and Menzel 2018, among others).