A.3.2 Creating association lists
An assocation list is created with one of the following predicates:
- [semidet]empty_assoc(?Assoc)
 - Is true if Assoc is the empty association list.
 - [det]list_to_assoc(+Pairs, -Assoc)
 - Create an association from a list Pairs of Key-Value pairs. 
List must not contain duplicate keys.
- Errors
 domain_error(unique_key_pairs, List)if List contains duplicate keys
 - [det]ord_list_to_assoc(+Pairs, -Assoc)
 - Assoc is created from an ordered list Pairs of 
Key-Value pairs. The pairs must occur in strictly ascending order of 
their keys.
- Errors
 domain_error(key_ordered_pairs, List)if pairs are not ordered.