Some definitions of interest.
absval	Def |i| == if 0i i else -i fi
	Thm* x:. |x|
assoced	Def a ~ b == a | b & b | a
	Thm* a,b:. (a ~ b)  Prop
le_int	Def ij == j<i
	Thm* i,j:. (ij)

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