Def i=j == if i=j true ; false fi

Thm* i,j:. i=j

Def {i..j} == {k:| i k < j }

Thm* m,n:. {m..n} Type

Def Surj(A; B; f) == b:B. a:A. f(a) = b

Thm* A,B:Type, f:(AB). Surj(A; B; f) Prop

Def AB == B < A

Thm* i,j:. ij Prop

Def A == A False

Thm* A:Prop. (A) Prop