let p, q be Prime; :: thesis: ( not p - q is odd or p = 2 or q = 2 )
assume p - q is odd ; :: thesis: ( p = 2 or q = 2 )
then ( ( p is odd & q is even ) or ( p is even & q is odd ) ) ;
hence ( p = 2 or q = 2 ) by NUMBER06:2; :: thesis: verum