The `regexp-opt' function does exactly what my `dedukti-regexp-disjunct'
function did
Looking backward in compile buffer for a file name doesn't seem to be
the right thing to do

Better change the dedukti error messages to add the file name.
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Adding keybindings

I don't find any keymap for dedukti-mode so I suspect that generic-mode
don't make one. I will probably switch to a derive-mode some day.