f/		number of args given to f/
		1	2	3	4	5	6	7	8
valence of f	1	converge	n-do|while
	2	fold	seeded fold	recurrence
	3			seeded fold	recurrence
	4				seeded fold	recurrence
	5					seeded fold	recurrence
	6						seeded fold	recurrence
	7							seeded fold	recurrence
	8								seeded fold