refrain from default task_context for all protocol commands, e.g. relevant for "build_theories" to admit Session.shutdown;
@InProceedings{dawson-avocs07,
author = {Jeremy Dawson},
title = {Isabelle Theories for Machine Words},
booktitle = {Seventh International Workshop on Automated Verification of Critical Systems (AVOCS'07)},
pages = {15},
year = {2007},
editor = {Michael Goldsmith and Bill Roscoe},
series = {Electronic Notes in Theoretical Computer Science},
address = {Oxford},
month = Sep,
publisher = {Elsevier},
note = {to appear},
}