  We formalise the modal operators from the concurrent dynamic logics of Peleg,
Nerode and Wijesekera in a multirelational algebraic language based on relation
algebra and power allegories, using relational approximation operators on
multirelations developed in a companion article. We relate Nerode and
Wijesekera's box operator with a relational approximation operator for
multirelations and two related operators that approximate multirelations by
different kinds of deterministic multirelations. We provide an algebraic
soundness proof of Goldblatt's axioms for concurrent dynamic logic as an
application.
