d/dx is notation for “derivative of” and what follows is a 4-variable function that (I think) would graph to some kind of 4D shape. Though taking the derivative of that surface with respect to X should result in a 3D shape. I think the author knew just enough calculus to sorta get the gist of something that looks like it’s describing 4D/3D stuff to anyone else who’s taken high school or college calculus (e.g. me. I don’t know much higher math)
d/dx is notation for “derivative of” and what follows is a 4-variable function that (I think) would graph to some kind of 4D shape. Though taking the derivative of that surface with respect to X should result in a 3D shape. I think the author knew just enough calculus to sorta get the gist of something that looks like it’s describing 4D/3D stuff to anyone else who’s taken high school or college calculus (e.g. me. I don’t know much higher math)