 Introduction rules in natural deduction add complexity: the conclusions of instances of an introduction rule are formed by adding an operator to earlier formulas. In contrast, elimination rules simplify: the premisses of instances of elimination rules are formed by deleting operators to the conclusions (or, in \(\lor\)-E, to the hypotheses of the subproofs used). The \(\mathcal{L}\)-systems have no simplifying rules of this kind. Their place is taken by complexifying rules on the left-hand side. Thus, for example, the rule for \(\land\) in the antecedent allows a sequent