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L ogic A principle of inference which states that from the premise “If p, then q and r” [(p→ (q ∧ r)], we can conclude “if p and q, then r” [(p ∧ q) → r]. This inference is a strict implication and can be expressed in propositional logic as [p→ (q ∧ r)] ↔ [(p ∧ q) → r]. The reverse of this inference, which is also valid, is called exportation . “If q implies q, and r implies r, and if p implies that q implies r, then pq implies r. This is the principle of importation.” Russell, Principles of Mathematics ... log in or subscribe to read full text