 \(\Peirce(t,c,q) = 1\) can be read ‘\(q\) is true at \(t\) in the chronicle \(c\)’. A formula \(q\) is said to be Peirce-valid if and only if \(\Peirce(t,c,q) = 1\) for any \(t\) in any \(c\) in any branching time structure (TIME,\(\le\),C) and any valuation function TRUE.