The notation also allows for introducing or subtracting a relentless quantity c for the roll. When an sum is included, the notation is nds+c or nDs+c; one example is, 3d6+four instructs the player to roll 3 6-sided dice, calculate the full, and increase 4 to it. Disphenoids, an infinite list of tetrahedra made from congruent non-normal triangles: