Use the two derived inference rules whose complete proofs were supplied in (d). The following logical derivation has no nested hypothetical subproofs:
1 P → Q premise
2 Q → R premise
3 P → (Q → R) → creation from 2
4 (P → Q) → (P → R) → distribution from 3
5 P → R →-elim, 1 and 4The creation instance takes and . The distribution instance takes . The metarules are justified in (d); this requested flat use does not secretly invoke implication introduction rule in one of its own lines.
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