GitLab

add a version of [cancel] that works with goals of the form [_ |- pvs _]; and use that for the barrier proof

write tactics to move particular assertions to the front, and to introduce a (*) while taking paticular assertions to the left/right

I talked with Christian, he is not the original author and forgot where it came
from, probably some coq-club mail.

Contrary to destruct_conj from Program.