  Expressing attack-defence trees in a multi-agent setting allows for studying
a new aspect of security scenarios, namely how the number of agents and their
task assignment impact the performance, e.g. attack time, of strategies
executed by opposing coalitions. Optimal scheduling of agents' actions, a
non-trivial problem, is thus vital. We discuss associated caveats and propose
an algorithm that synthesises such an assignment, targeting minimal attack time
and using the minimal number of agents for a given attack-defence tree. We also
investigate an alternative approach for the same problem using Rewriting Logic,
starting with a simple and elegant declarative model, whose correctness (in
terms of schedule's optimality) is self-evident. We then refine this
specification, inspired by the design of our specialised algorithm, to obtain
an efficient system that can be used as a playground to explore various aspects
of attack-defence trees. We compare the two approaches on different benchmarks.
