 Taken in isolation, this is indistinguishable from \(\Delta\), but the two operators together interact differently, for while \(\dashv \Delta\Delta p\) and \(\dashv \nabla\nabla p\), both \(\vdash \Delta\nabla p\) and \(\vdash \nabla\Delta p\). Łukasiewicz compares them to twins which are indistinguishable separately but distinguishable together. Similar twins are the necessity operator \(\Gamma\) and its counterpart (with values 3434), and indeed the two intermediate truth-values 2 and 3.