Re: [isabelle] problem with opening proof



Hi Chris,

> fix ...
> assume ... and ...
> thus "EX x y. ..."
> proof

"proof" is short for "proof default", where the "default" method performs:

1. introduction using a suitable predeclared rule if no facts are
chained in.

2. elimination using a suitable predeclared rule if any facts are
chained in.

So in your case it fails because there are no suitable elimination rules
for your assumptions.

What you can try instead:

> fix ...
> assume P: ... and Q: ...
> show "EX x y. ..."
> proof
>   from P Q ...

or perhaps

> fix ...
> assume ... and ...
> show "EX x y. ..."
> proof (intro exI)

Hope this helps
	Florian

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