correctly resolved conflict...
rely implicitly on the fact that a tuple is a tuple of fresh variants

And therefore, projections on the same n-term must be variants of each other.

This makes sure we no longer do invalid things like:

Given a valid term <t^1,...,t^n>\G, talk about the invalid term t\G.

Moreover, it clarifies the relationship between Lemma 8 and Lemma 17.

Also: add a missing {r/y} to the proof.