*To*: John Munroe <munddr at gmail.com>*Subject*: Re: [isabelle] A simple lemma*From*: Viorel Preoteasa <viorel.preoteasa at abo.fi>*Date*: Fri, 07 Sep 2012 19:39:12 +0300*Cc*: cl-isabelle-users at lists.cam.ac.uk*In-reply-to*: <CAP0k5J66Q2ZDbNw9yegpiZrvUa14swu=HeON8cjLD2HDqh7XkA@mail.gmail.com>*References*: <CAP0k5J66Q2ZDbNw9yegpiZrvUa14swu=HeON8cjLD2HDqh7XkA@mail.gmail.com>*User-agent*: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:15.0) Gecko/20120824 Thunderbird/15.0

Hello, If you rewrite it like: lemma "F = G --> (EX a b. a = b or (F a = G a & F b ~= G b))" you would see why it is true. Viorel On 9/7/12 7:25 PM, John Munroe wrote:

Hi, Does anyone know why the following lemma is provable? lemma "F = G --> (EX a b. a ~= b --> F a = G a & F b ~= G b)" by auto If F and G are equal, then F x = G x for all x. So how come the above is provable? Thanks a lot for your time. John

**References**:**[isabelle] A simple lemma***From:*John Munroe

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