The key point here is that just because `x_ptr` and `&y[0]` point to the same *address*, that does not make them *the same pointer*, i.e., they cannot be used interchangeably:
`&y[0]` points to the first element of `y`; `x_ptr` points past the end of `x`.
-If we replace `*x_ptr = 23` by `*&y[0] = 0`, we change the meaning of the program, even though the two pointers have been tested for equality.
+If we replace `*x_ptr = 23` by `*&y[0] = 23`, we change the meaning of the program, even though the two pointers have been tested for equality.
This is worth repeating: