Add a Notation for `sn`: strongly normalizing.
As requested by @jung in https://gitlab.mpi-sws.org/FP/iris-coq/merge_requests/65
I made this a notation to avoid unfolding issues.
As requested by @jung in https://gitlab.mpi-sws.org/FP/iris-coq/merge_requests/65
I made this a notation to avoid unfolding issues.