Hi Chantal,

| I wonder if there is a mistake in the specification of the CHOOSE rule
| in HOL-Light
| <http://www.cl.cam.ac.uk/~jrh13/hol-light/HTML/CHOOSE_UPPERCASE.html>.

Yes, indeed there is; thanks for pointing that out. I've now fixed the
documentation page above. I also took the chance to propagate a few
other unrelated changes from the Help/*.doc files where I hadn't kept
the online html in step.

| Fortunately, when I try to apply this rule in HOL-Light with the two
| premisses above, I get the following error: "Exception: Failure
| "CHOOSE".". That is why I conclude that the specification would be false
| rather than that HOL-Light would be unsound.

Yes, since the CHOOSE rule is derived from more primitive rules anyway,
the correct (or at least, not too weak) side-conditions get enforced
automatically by the derivation. But still, it was bad not to have the
documentation right for something pretty elementary.

| Perhaps in the specification, one must add that v should not be free in s?

I think that is correct, and that's how I've changed the documentation.

John.

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