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In general, we can calculate the joint distribution of the endogenous variables of a structural casual model (SCM) as follows
$$
P(X, X_1, \dots, X_n) = \prod_i = P(X_i \mid \text{parent}(X_i))
$$
where $\text{parent}(X_i)$ is the parent node of $X_i$ in the graphical representation of the SCM...