Index to enforce non-overlapping ranges?

Academic question here:
Given a table with a pair of any sort of line-segment-esqe range  
delimiter columns, is it possible to build a unique index to enforce  
non-overlapping ranges? Such as:
create table test(    id int not null primary key,    low_value int not null,    high_value int not null);
Can one build an index to enforce a rule such that no (low_value,  
high_value) range is identical or overlaps with another (low_value,  
high_value) range described by the table? And, more interestingly,  
what about for ranges of dates / timestamps as opposed to simple  
integers?
I can see how a trigger on insert or update could enforce such a  
constraint [ probe the table for an existing overlapping row, and  
raise exception one exists ], but can such an activity be performed  
with fewer lines using some sort of r-tree index?

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James Robinson
Socialserve.com