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 (-5[1])is to consider an infinite square grid and to cross out repeated (10[1])elements when considering successive diagonals. For showing a number (10[1])did not belong to this set, Hippasus was supposedly drowned by the (-5[1])Pythagoreans. The decimal expansions of elements of this set either terminate (-5[1])or have a repeating sequence. (10[1])For 10 points, name this (10[1])set denoted by a blackboard Q which is contrasted (-5[1])with the irrational (10[2]0[1])numbers. (10[1])■END■ (10[1])