Why can we omit the first dimension of a multidimensional array when we are passing it to a function

Question

Why can we omit the first dimension of a multidimensional array when we are passing it to a function?

In my programming class, we were told what when passing a multidimensional array to a function we can omit first dimension, for example, a[10][15][20] can be passed as a[][15][20].

Why?

Answer 1

Because the array will decay to pointer and to calculate offset to the elements of the array you do not need to know the innermost dimension. Offset to a[i][j][k] is i*nj*nk+j*nk+k (where nj and nk are corresponding dimensions).