n51.
The advantage of parallel currencies within a single economy does not persist into a case for the presence of, say, three currencies. This would triple the number of exchange options (from the single exchange available in the case of two currencies) and would also introduce an economic “layering” of society, which would be quite different from the localisation we need. Parallel currencies are discussed with guarded approval by James Robertson (1998), Transforming Economic Life, pp 56–7.