Using a lemma of D. E. Knuth [J. of combin. theory(B)16
(1974)42—46]
we present a simple proof of the following theorem of Horák Peter et al. (cf. MR. 84g: 05069 MR. 42~#1718; MR. 44~#2668): Let D be a nontrivial strongly connected digraph. Then for any ν∈V(D) there is a vertex u(ν)≠ν such that D-u(ν) is unilateral and that ν can reach evcry vertex in D-u(ν).