SIDED DICE NO FURTHER A MYSTERY

The intervals' symmetry can be both like ABBA and CDDC, as turned out to be the situation, or like ABCD and DCBA, the place the intervals of one die reverse the intervals of one other die.Recognize that incorporating the rolls of A and D generates a random range between 1 and 20, making sure that A and D together simulate a d20, or maybe a + D = d2