docs: def Aitken(s):
  	"""Accelerate the convergence of the a series
  	using Aitken's delta-squared process (SCIP calls it Euler).
  	"""
  	def accel():
  		s0, s1, s2 = s >> item[:3]
  		while 1:
  			yield s2 - (s2 - s1)**2 / (s0 - 2*s1 + s2)
  			s0, s1, s2 = s1, s2, next(s)
  	return accel()