# property[].description
Indicates that the code is abstract - only intended to be used as a selector for other concepts

# concept[].definition
Operations that can be used to associate concepts in a terminology.

# concept[].concept[].definition
Form the set-difference with this value, i.e., exclude this element or set from the resulting set.

# concept[].concept[].definition
Form the union with this value, i.e., include this element or set in the resulting set.

# concept[].definition
Form the convex hull with the value. The convex hull is defined over ordered domains and is the smallest contiguous superset (interval) that of all the operand sets.

# concept[].definition
Form the periodic hull with the value. The periodic hull is defined over ordered domains and is the periodic set that contains all contiguous supersets of pairs of intervals generated by the operand periodic intervals.