incrementing a pointer to an array

The following portion is from c-faq.com - comp.lang.c FAQ list ·
Question 6.13

int a1[3] = {0, 1, 2};
int a2[2][3] = {{3, 4, 5}, {6, 7, 8}};
int *ip; /* pointer to int */
int (*ap)[3]; /* pointer to array [3] of int */\

ap = &a1;
printf("%d\n", **ap);
ap++; /* WRONG */

Here why is incrementing ap ie 'ap++' mentioned as WRONG ? Isn't it
similar to
int i_int = 100;
int *p = &i_int;
p++;

Here we cannot dereference 'p' but incrementing 'p' only once, is
allowed. Similarly,

ap is assigned '&a1'. Then we increment ap only once. Why is this
WRONG ?

Kindly clarify.

Thanks
V.Subramanian
.