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Random walks on trees. Discret. Math. 30(3): 269-276 (1980) - Robert A. Proctor, Michael E. Saks, Dean G. Sturtevant:
Product partial orders with the sperner property. Discret. Math. 30(2): 173-180 (1980) - László Surányi:
On a generalization of linecritical graphs. Discret. Math. 30(3): 277-287 (1980)