*To*: Simon Winwood <sjw at cse.unsw.edu.au>*Subject*: Re: [isabelle] Calculation-style reasoning, reflexive equality, and strangeness*From*: Makarius <makarius at sketis.net>*Date*: Tue, 14 Sep 2010 14:26:33 +0200 (CEST)*Cc*: isabelle-users at cl.cam.ac.uk*In-reply-to*: <AA04E90F-85FA-42C5-A885-F3F696BE5DE6@cse.unsw.edu.au>*References*: <AA04E90F-85FA-42C5-A885-F3F696BE5DE6@cse.unsw.edu.au>*User-agent*: Alpine 1.10 (LNX 962 2008-03-14)

On Tue, 14 Sep 2010, Simon Winwood wrote:

Consider the following proof lemma "X = Y" proof - have "X = z" sorry also have "\<dots> = z" by simp also (* want X = z, get X = X *) After the 'also', calculation is "X = X", rather than the "X = z" you would expect. We figured that the reason for this is that the chaining rule is forw_subst [| a = b; P b |] ==> P a which, when unified with the above two rules gives P == %x. x = x hence P X == X = XI suppose this is a corner case, but it could be solved by tryingtrans before forw_subst.

Makarius

**References**:**[isabelle] Calculation-style reasoning, reflexive equality, and strangeness***From:*Simon Winwood

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