Here, the selection of the formula D for the focus can be taken as selecting among several macro-rules: this derivation illustrates one such macro-rule: the inference rule with conclusion ` Θ,D ⇑ · and with n ≥ 0 premises ` Θ,D ⇑ N1, . . . , ` Θ,D ⇑ Nn (where N1, . . . ,Nn are negative formulas). We shall say that this macro-rule is positive. Similarly, there is a corresponding negative macro-r...