Nuprl - Proof: bij imp exists inv2 1 2 1

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At: bij imp exists inv2 1 2 1

1. A : Type
2. B : Type
3. f : A

B
4.

a1,a2:A. f(a1) = f(a2)

a1 = a2
5.

b:B.

a:A. f(a) = b
6.

b:B.

!a:A. f(a) = b
7. g : B

A
8.

b:B. f(g(b)) = b
9. x : A

g(f(x)) = x

By:	BackThru: Hyp:4

Generated subgoal:

1 f(g(f(x))) = f(x)
1 step

About:

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