Support mixing of single-tape expressions with multitape expressions
It seems quite conventional in linguistics for instance to write [abc]
to mean a|a + b|b + c|c
. That's really nice on the input, but also on the output: writing [a|ab|bc|c]
etc. is really ugly.
We should also try to recognise things like [abc]|\e
and write them as such instead of a|\e, b|\e, c|\e
.
I expect it is when adding that we want to mix single-tape with multitape. See partial_identity
to go multitape.