User blog comment:Denis Maksudov/M-notation (new version)/@comment-24920136-20160621003904/@comment-28606698-20160628215232

 In this notation (a) times.

 in this notation f_w (w) used only as subscript, and   it  is implied default, that  f (a) exists as first level, where (a) is nonnegative integer

 For example f_w2 (a)=f_(w+a)  (a)=f_(f_0^a (w))  (a)