Z Specification (continued)
control = no_change transitions
no_change = { s : STATE; e : EVENT � (s, e) s }
transitions = { (patients, enter) fields,
(fields, select_patient) patients, (fields, enter) setup,
(setup, select_patient) patients, (setup, select_field) fields,
(ready, select_patient) patients, (ready, select_field) fields,
(ready, start) beam_on, (ready, interlock) setup,
(beam_on, stop) ready, (beam_on, interlock) setup }