add lemmas about seq

Adding a couple of lemmas about seq. Please let me know if you prefer bigger MRs. I have a fair amount of stuff that I want to merge eventually.

Please let me know if you prefer bigger MRs.

Small MRs are ideal. They are rather easy to review compared to big ones, and if there is bikeshedding about one part of the MR, it does not block the whole MR.

resolved all threads

added 1 commit

• ffcb6d4d - Apply 1 suggestion(s) to 1 file(s)

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resolved all threads

added 1 commit

• a9167769 - Apply 1 suggestion(s) to 1 file(s)

Compare with previous version

@jung Feel free to merge if you have no more comments.

mentioned in commit 6ac98356

merged

LGTM, thanks!