C.28.MR:5.3 - A definite intervention answer with an indefinite baseline

Take real-valued variables with mechanisms X=Y and Y=X. Every equal pair satisfies the baseline equations. Without another condition, the model does not determine the baseline value of Y.

Replace the first mechanism by X=1. The retained equation now gives Y=1. That intervention consequence is determined. A difference from the baseline remains undetermined because the baseline’s value or distribution has not been supplied.

If the requested result is only Y under the intervention, return one. If the requested result is its change from natural behavior, return the missing baseline condition. Resolving the first question does not require inventing that condition.