def accsum(it):
"""Yield accumulated sums of iterable: accsum(count(1)) -> 1,3,6,10,..."""
return drop(1, ireduce(operator.add, it, 0))
def fibonacci():
"""Generate fibonnacci serie"""
get_next = lambda (a, b), _: (b, a+b)
return (b for (a, b) in ireduce(get_next, count(), (0, 1)))