I hit three-thousand something -rare indeed- and the majority of the hits were (as you thought) academic. For example, and note the date here, in R. S. Peters on Punishment by John Kleinig British Journal of Educational Studies, Vol. 20, No. 3 (Oct., 1972), pp. 259-269"Indeed, so much is covered, that it can be wondered whether there is any univocity in the notion of a rule and whether the notion of a rule serves as an...."