 are actually true. (And, indeed, these nested counterfactuals follow from the system of equations, on the causal modeling semantics.) However, on many semantics for counterfactuals, this nested counterfactual does not follow from the counterfactuals given in (3.4.1) above. We might attempt to reduce nested counterfactuals like these to counterfactuals with conjunctive antecedents by appeal to a principle of exportation, according to which \(\phi \boxto (\psi \boxto \chi)\) follows from \((\phi \wedge \psi) \boxto \chi\). However, on the causal modeling semantics, exportation is not valid in general. Take the causal model above. Assuming counterfactuals with necessarily false antecedents are vacuously true,