calculation NumberRule1a:
	0 * a -> 0
calculation NumberRule1b:
	a * 0 -> 0

calculation NumberRule2a:
	1 * a -> a
calculation NumberRule2b:
	a * 1 -> a

calculation NumberRule3a:
	a - a -> 0
calculation NumberRule3b:
	(-1 * a) + a -> 0
calculation NumberRule3c:
	a +- a -> [0, 2*a]

expansion NumberRule4:
	a +- b -> [a + b, a - b]

calculation NumberRule5a:
	a + 0 -> a
calculation NumberRule5b:
	0 + a -> a
calculation NumberRule5c:
	a - 0 -> a
calculation NumberRule5d:
	0 - a -> -1 * a
calculation NumberRule5e:
	a +- 0 -> a

expansion NumberRule7:
	a + a -> 2 * a