A non associative container should implement at least empty-p,
 empty, insert-item and delete-item. 
| abstract-container | Inherited by all container classes, this is a good place to | 
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| ordered-container-mixin | |
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| unordered-container-mixin | 
| delete-list | Deletes each item in the list from the container. | 
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| insert-list | Adds each item in the list to the container in an | 
| iterate-elements | 
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