Some remarks on the theory of graphs
P. Erdös · Bulletin of the American Mathematical Society · 1947
Recently very much more general theorems have been proved by Grünwald and Milgram. 3 They in fact proved (among others) that the condition that G' contains no closed directed path is superfluous.We suppress the proof of Theorem Ha since it is essentially the same as that of Theorem II.(We only remark that a connected to b by a line directed from a to & should be replaced by a divides b.)