Hello, how can i prove the following: ( THE A. {a. f a = {c1, c2, c3}} = {a. f a = A} ) = {c1, c2, c3} ? Thank you! -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mailmanbroy.informatik.tu-muenchen.de/pipermail/isabelle-dev/attachments/20130522/a0317d98/attachment-0001.html>