Yury GlazkovAlexey BaburinEdward GimadiFederico Della CroceVangelis Th. PaschosApproximation algorithms for 2-Peripathetic Salesman Problem with edge weights 1 and 2.35-36200627Electron. Notes Discret. Math.https://doi.org/10.1016/j.endm.2006.08.043db/journals/endm/endm27.html#GlazkovBGCP06