initialize lists as empty
new action id args to sys_trans_from_ts

sys_action_ids, env_action_ids
default to None
replace arg: env_vars -> env_action_ids of env_trans_from_sys_ts
new action id args to env_trans_from_env_ts
make unrealizable switched system test of synth a function
prepend 'none' action with action var name

To avoid mixing env and sys 'none' actions.
Note that overlap of the env and sys action sets is not checked anywhere yet.
So the user is expected to ensure env and sys actions are disjoint sets.
bugfix: don't mutex singleton of actions
represent mutexed actions of sys OpenFTS by int var

by using action_ids, env_action_ids, sys_action_ids in sys_open_fts2spec
represent mutexed actions of env OpenFTS by int var

using action_ids, env_action_ids, sys_action_ids in sys_open_fts2spec
bugfix: if no sys actions, then they can't block env
tests for OpenFTS actions as bool, int vars
update switch example to synth.synthesize signature
update examples for actions represented by int var

If more than 2 actions are defined, then by default mutual exclusion is assumed.
So an int variable models them in GR(1).
If they appear in the spec, they should be in one of the following forms:

    - act = action_value
    - eact = action_value

depending on whether a sys or env action is involved.

This requires that the user anticipate internal behavior of synth.
To be avoided by replacing lone occurrences of 'action_value' in the logic part of the spec by 'act = action_value' or 'eact = action_value', as appropriate.
constrain the initial states of some examples

to make them human readable, otherwise their educational role is undermined.