  The extension of counterfactual causal graphic model with three variables of
vertex set in directed acyclic graph (DAG) is discussed in this paper by
extending two- value distribution to three-value distribution of the variables
involved in DAG. Using the conditional independence as ancillary information, 6
kinds of extension counterfactual causal graphic models with some variables are
extended from two-value distribution to three-value distribution and the
sufficient conditions of identifiability are derived.
