@article{10_4064_aa_63_3_205_210,
     author = {G\"unther Wirsching},
     title = {An improved estimate concerning 3n+1 predecessor sets},
     journal = {Acta Arithmetica},
     pages = {205--210},
     publisher = {mathdoc},
     volume = {63},
     number = {3},
     year = {1993},
     doi = {10.4064/aa-63-3-205-210},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-63-3-205-210/}
}