Nuprl - Proof: bij imp exists inv2 1 2

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At: bij imp exists inv2 1 2

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

(

x:A. g(f(x)) = x) & (

y:B. f(g(y)) = y)

By:

Analyze

Generated subgoal:

1 9. x : A
g(f(x)) = x
2 steps

About:

IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html