A hollow quadrangular prism, comprising:
- first, second, third and fourth rigid right triangular prisms,
- each right triangular prism having an upper and a lower base having identical shapes of an obtuse and scalene triangle,
- each right triangular prism having a rectangular front lateral face, a rectangular rear lateral face and a rectangular bottom floor, located between and perpendicular to the upper and lower bases, the obtuse triangles of the upper and lower bases flare to the bottom floor,
- wherein the rectangular front lateral face and the rectangular rear lateral face of each right triangular prism is covered by a reflective material of visible light,
- wherein the upper bases of the first to fourth right triangular prisms are on a same first plane and the lower bases of the four right triangular prisms are on a same second plane,
- wherein the bottom floors of the first and third right triangular prisms are on a same third plane and immediately adjacent each other, and the front lateral face of the first right triangular prism and the rear lateral face of the third right triangular prism are adjacent each other, wherein the bottom floors of the second and fourth right triangular prisms are on a same fourth plane and immediately adjacent each other, and the front lateral face of the second right triangular prism and the rear lateral face of the fourth right triangular prism are adjacent each other,
- wherein the third plane and the fourth plane are non-parallel to each other and define a bisector plane between them, wherein the first to fourth right triangular prisms are located between the third and fourth planes, wherein the first and second right triangular prisms are symmetrical with respect to the bisector, and the third and fourth right triangular prisms are symmetrical with respect to the bisector, and
- wherein a height of the upper base triangle of the first right triangular prism, defined by a perpendicular distance from the bottom floor of the first right triangular prism to an intersection line of the front and rear lateral faces of the first right triangular prism, is identical to a height of the upper base triangle of the third right triangular prism, defined by a perpendicular distance from the bottom floor of the third right triangular prism to an intersection line of the front and rear lateral faces of the third right triangular prism.