Some definitions of interest.
increasing	Def increasing(f;k) == i:(k-1). f(i)<f(i+1)
	Thm* k:, f:(k). increasing(f;k)  Prop
inject	Def Inj(A; B; f) == a1,a2:A. f(a1) = f(a2)  B  a1 = a2
	Thm* A,B:Type, f:(AB). Inj(A; B; f)  Prop
int_seg	Def {i..j} == {k:| i  k < j }
	Thm* m,n:. {m..n}  Type
nat	Def  == {i:| 0i }
	Thm*   Type

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