 If \(i\) is an opponent of \(k\), then \(i\)’s individual strategy \(s_{i j}\) may be characterized as a union of strategy combinations \(\bigcup\{\boldsymbol{s}_{-k}\mid s_{ij}\in \boldsymbol{s}_{-k}\} \in \mathfrak{F}_k\), and so \(k\)’s marginal probability for \(i\)’s strategy \(s_{i j}\) may be calculated as follows: