Editing Sprague–Grundy theorem (section)

===Nimbers===
The special names <math>*0</math>, <math>*1</math>, and <math>*2</math> referenced in our example game are called '''''[[nimber]]s'''''.  In general, the nimber <math>*n</math> corresponds to the position in a game of nim where there are exactly <math>n</math> objects in exactly one heap.  
Formally, nimbers are defined inductively as follows:  <math>*0</math> is <math>\{\}</math>, <math>*1 = \{*0\}</math>, <math>*2 = \{*0, *1\}</math> and  for all <math>n \geq 0</math>, <math>*(n+1) = *n \cup \{*n\}</math>.

While the word ''nim''ber comes from the game ''nim'', nimbers can be used to describe the positions of any finite, impartial game, and in fact, the Sprague&ndash;Grundy theorem states that every  instance of a finite, impartial game can be associated with a ''single'' nimber.