I'm in the middle of completing a proof, and need to show that b=a. I already have a=b. I think this should be trivial, however, I cannot find a way to do it inside the system.

Using the programs "Ana-Con" feature, it does indeed suggest that this is true within the system, but I can't find a way to do this without using this shortcut.

Anyone have any suggestions?

1 Answer 1


Looks like you're using the text "Language, Proof and Logic." I have the book but not the software, but couldn't you just use = intro and = elim as in:

  1. a=b.
  2. b=b. =intro
  3. b=a. =elim 1,2

Basically, just treat "identical to b" as a predicate (which it actually is) and this proof should work.

You don't need to cite a line for =intro (per comment)

  • What Kevin Holmes suggested works, however you don't have to cite any line for =intro. It rejected my citation When it asks for the rule, make sure you don't have any other line highlighted just click: intro =
    – user15152
    Jul 1, 2015 at 12:30

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