May be it will help.
Let we have n-dimensional "parallelepiped".
part 1: 0< x_1< 1, 0< x_2< 1,... 0< x_{n-1}< 1, 0< x_n< 1,
part 2: 0< x_1< 1, 0< x_2< 1,... 0< x_{n-1}< 1, 1< x_n< 2,
part 3: 0< x_1< 1, 0< x_2< 1,... 1< x_{n-1}< 2, 0< x_n< 1,
part 4: 0< x_1< 1, 0< x_2< 1,... 1<...