An empty trie.

find term n trie

Find the value associated with the key term in trie. term is valid in a context of size n. Return None if no value can be found under the key term.

add_new term n a trie

Add the key value pair (term, a) where term is valid in a context of size n to trie. Return the new trie or a value which has already been stored under the key term.