Hayes, S. C., J. M. Devany, B. S. Kohlenberg, A. J. Brownstein, and J. Shelby. “Stimulus Equivalence and the Symbolic Control of Behavior”. Mexican Journal of Behavior Analysis, vol. 13, no. 3, May 2011, pp. 361-74, doi:10.5514/rmac.v13.i3.25325.