| If three letters together represent a single sound, they constitute a trigraph, such as tch in catch and sch in schmaltz. |
| The modeling of new trigraphs with decision trees is very simple: each state of the trigraph is positioned at the root node of the tree corresponding to the same state position and the same central letter. |
| There are many ways to tie the parameters of trigraph models, as well as many ways to cluster models. |
| The same would be true if digraph or trigraph frequencies were plotted for a sufficiently long ciphertext. |
| In this paper, we propose to build trigraph models and to share parameters between these trigraphs. |
| Then each state descends its belonging tree, answering questions on the trigraph contexts, until it reaches a node where a cluster is positioned. |
