Testing invalidation due to overwrite:
x + y = 1 (original)
x - y = -1 (original)
x + y = 1 (original)
x - y = -1 (original)
x + y = 1 (original)
x - y = -1 (overwritten)
x + y = 1 (overwritten)
x - y = -1 (overwritten)
x + y = 1 (original)
x - y = -1 (original)
x + y = 1 (original)
x - y = -1 (original)
x + y = 1 (original)
x - y = -1 (overwritten)

Testing invalidation due to delete:
x + y = 1 (from proto1)
x - y = -1 (from proto1)
x + y = 1 (from proto1)
x - y = -1 (from proto1)
x + y = 1 (from proto1)
x - y = -1 (from proto2)
x + y = 1 (from proto2)
x - y = -1 (from proto2)

Testing invalidation due to shadowing:
x + y = 1 (from proto2)
x - y = -1 (from proto2)
x + y = 1 (from proto2)
x - y = -1 (from proto2)
x + y = 1 (from proto2)
x - y = -1 (from proto1)
x + y = 1 (from proto1)
x - y = -1 (from proto1)