[Agda] Weird termination problem

[Jason -Zhong Sheng- Hu]

I once saw someone else's code where termination checker also failed with no good reason. the author worked around it by turning on K. could you see if K works around it for you?

Thanks,
Jason Hu
https://hustmphrrr.github.io/
________________________________
From: Agda <agda-bounces at lists.chalmers.se> on behalf of Thorsten Altenkirch <Thorsten.Altenkirch at nottingham.ac.uk>
Sent: August 15, 2020 9:25 AM
To: agda at lists.chalmers.se <agda at lists.chalmers.se>
Subject: [Agda] Weird termination problem


Hi,



I just transferred some code form my lecture notes to my book draft and now the termination checker complains where there was no problem before:



thm : {P : Form} → ([] ⊢ P) ⇔ ⊢sk P

proj₁ thm d = skC→sk (⊢→⊢skC d)

proj₂ thm SS = S-d

proj₂ thm KK = K-d

proj₂ thm (app d e) = app (proj₂ thm d) (proj₂ thm e)



so here ⊢sk P is inductively defined and there should be no problem – and indeed there wasn’t before. But now



Termination checking failed for the following functions:

  thm

Problematic calls:

  proj₂ thm e



I can’t make any sense out of it. Has anybody an inkling what could have happened or any advice what I could do to fix it.



I can prove the <= direction on its own with no problems. The definition of ⇔ is exactly the same as before and it doesn’t help if I expand it. Also the definition of products is the same as before.



If you want to have a look at the code please let me know – I will give you access to the repo.



Cheers,

Thorsten



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