Every non-trivial norm on this set is either the standard absolute value or a p-adic norm according to Ostrowski's theorem. This set is the smallest field with characteristic zero. The standard method of proving this set is countable is to consider an infinite square grid (10[1])and to cross out (10[1])repeated (10[1])elements (10[1])when considering (10[1])successive diagonals. For showing a number did not (10[1])belong to this set, Hippasus was supposedly drowned by the Pythagoreans. The (10[1])decimal expansions of elements of this set either terminate or have a repeating (-5[1])sequence. For 10 points, name this set denoted by a blackboard Q which is contrasted with the irrational numbers. (10[1])■END■