!! Warning: Unexpected token during syntax-highlighting: '₁'
!! Alectryon's lexer isn't perfect: please send us an example.
!! Context:
forall x y : A s,
cong_ker f s x y ->
(f s x; ❘ (x; 1) ❘₋₁
Yup, I think we won't really be able to fix this — notations can contain arbitrary sequences, basically, so the best might just be to turn that warning off and wait until Coq can do the fontification for us.
https://github.com/HoTT/HoTT/runs/2353786837?check_suite_focus=true#step:5:2352