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Sometimes it is useful to have a tactic which does nothing. I've tried to search "empty tactic" or "null tactic" but these do not give me the answer.

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1 Answers1

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The tactic you are looking for is idtac, short for "identity tactic"

 Tactic idtac (ident ​| string​ | natural)*

Leaves the proof unchanged and prints the given tokens. Strings and naturals are printed literally. If ident is an Ltac variable, its contents are printed; if not, it is an error. source

You can give idtac arguments, which are useful for debugging.

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