Use 0 and 1 for booleans:
    - to free up t and f for other types
    - more common mapping for scripting langs like Perl?
Other types that might be considered:
    - tuples: (1,2,2,3)
    - sets: <1,2,3>
    - Complex numbers: ???
    - rational numbers: R1/2,
    - date: dyyyy-mm-dd,
    - timestamp: dyyyy-mmddThh:mm:ss.sss+hh:mm, # 3339?
    - timestamp: jddddddd.ddddd±hh:mm, # julian day version?
    - week: Dyyyy-Www,