abs(n real) real: {
	n real < 0.0 real boolean -> -n real, n real
} void

fac(n natural) natural: {
	n natural == 1 natural boolean ->
		1 natural,
		n natural * fac(n natural -1 natural) natural
} void

d date: [15 mar 2013] date -> {
	d date +
	[ - abs: ] vector string + abs(-100 real) real +
	[fac: ] vector string + fac(3 natural) natural +
	[\n] vector string
} vector string output