Some definitions of interest.
decidable	Def Dec(P) == P  P
	Thm* A:Prop. Dec(A)  Prop
int_seg	Def {i..j} == {k:| i  k < j }
	Thm* m,n:. {m..n}  Type
rel_star	Def (R^*)(x,y) == n:. x R^n y
	Thm* T:Type, R:(TTProp). (R^*)  TTProp
nat	Def  == {i:| 0i }
	Thm*   Type

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