$\"\"$

The equation is $\"\"$ .

$\"\"$

$\"\"$ .

$\"\"$ is a plane one unit above the $\"\"$ - plane.

$\"\"$ is a plane one unit below the $\"\"$ - plane.

$\"\"$

$\"\"$ is a plane one unit above the $\"\"$ - plane.

$\"\"$ is a plane one unit below the $\"\"$ - plane.