The four-dimensional Martínez Alonso–Shabat equation: Reductions and nonlocal symmetries

We consider the four-dimensional integrable Martínez Alonso–Shabat equation and list three integrable three-dimensional reductions thereof. We also present a four-dimensional integrable modified Martínez Alonso–Shabat equation together with its Lax pair.We further construct an infinite hierarchy of commuting nonlocal symmetries (and not just the shadows, as it is usually the case in the literature) for the Martínez Alonso–Shabat equation.