docs: def piGenGosper():
      """A generator function that yields the digits of Pi
      """
      z = ((1,0,0,1),1)
      while True:
          lft = __lfts(z[1])
          n = int(__next(z))
          if __safe(z,n):
              z = __prod(z,n)
              yield n
          else:
              z = __cons(z,lft)