rdf_keys_in_literal_map(+Map, 
+Spec, -Answer)Realises various queries on the key-set:
- all
 - Unify Answer with an ordered list of all keys.
 
- key(+Key)
 - Succeeds if Key is a key in the map and unify Answer 
with the number of values associated with the key. This provides a fast 
test of existence without fetching the possibly large associated value 
set as with rdf_find_literal_map/3.
 
- prefix(+Prefix)
 - Unify Answer with an ordered set of all keys that have the 
given prefix. Prefix must be an atom. This call is intended 
for auto-completion in user interfaces.
 
- ge(+Min)
 - Unify Answer with all keys that are larger or equal to the 
integer Min.
 
- le(+Max)
 - Unify Answer with all keys that are smaller or equal to the 
integer Max.
 
- between(+Min, +Max)
 - Unify Answer with all keys between Min and Max 
(including).