Mirko Hornák Jakub Przybylo Mariusz Wozniak A note on a directed version of the 1-2-3 Conjecture. 472-476 2018 236 Discret. Appl. Math. https://doi.org/10.1016/j.dam.2017.11.016 https://www.wikidata.org/entity/Q122979018 db/journals/dam/dam236.html#HornakPW18