 First, recall that “\(\amp\)” is an analogue of the English connective “and”. Intuitively, one can deduce a sentence in the form \((\theta \amp \psi)\) if one has deduced \(\theta\) and one has deduced \(\psi\). Conversely, one can deduce \(\theta\) from \((\theta \amp \psi)\) and one can deduce \(\psi\) from \((\theta \amp \psi)\):