sentences:  The equivalent nim heap size of a position may be calculated as the minimum excluded value of the equivalent sizes of the positions that can be reached by a single move.For subtract-a-square positions of values 0, 1, 2, ... the equivalent nim heap sizes are
  In particular, a position of subtract-a-square is cold if and only if its equivalent nim heap size is zero.It is also possible to play variants of this game using other allowed moves than the square numbers.