Minor typo in Motulsky and Mahan 1984.

Alexander Ross, Department of Pharmacology at the University of Cincinnati, pointed out a minor mistake in Motulsky, H. J. & Mahan, L. C. The kinetics of competitive radioligand binding predicted by the law of mass action. Molecular Pharmacology 25, 1–9 (1984). The error is in the first part of the mathematical appendix:

The highlighted y-hat term should actually be an x-hat term. 

This is only a typo in creating and setting the manuscript, as the equations derived in the paper are correct, so all the pharmacological conclusions are also correct. 

Alexander Ross has provided his derivation of the equations here.