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.

For consistency's sake.

get rid of substitution in Case (use lambdas); introduce Match as derived form that involves binders

We no longer abuse empty strings for anonymous binders. Instead, we
now have a data type for binders: a binder is either named or
anonymous.