“…This The designs that do exist can be realized as residuals of symmetric designs, and the status of those with question marks is at present unknown. The ∄-marked (22,33,12,8,4) has recently been shown not to exist [1] (see also the exposition in [16]). Designs with the parameters marked with ⋪ do exist, but none are residuals of symmetric designs, the needed designs being ruled out by the Bruck-Ryser-Chowla theorem.…”