Correctly distinguish when multiple listeners exist
Comments in ground.rkt
Mostly cosmetic; improvements from yesterday's code review
Notes and improvements from code review
Introduce threads and send-ground-message to TCP driver.
Widen ground-level inertness detection to account for non-event ground-level gestalt.
Changes from code review
Simplify matcher-project
Ugh, stupid undefined-variable
Remove silly identity-projection efficiency hack.
Provide an identity for set-union