Before revision:  We exhibit a general model for absolute discrimination , and further show how addition of proofreading steps inverts the expected hierarchy of antagonism without fully cancelling it.
After revision:  We exhibit a simple analytic model of absolute discrimination displaying ligand antagonism, where antagonism strength is linear in distance from threshold. This contrasts with proofreading based models, where antagonism vanishes far from threshold and thus displays an inverted hierarchy of antagonism without fully cancelling it.