@article{JIS_2004__7_1_a6,
     author = {Schlage-Puchta,  Jan-Christoph and Spilker,  J\"urgen},
     title = {The greatest common divisor of two recursive functions},
     journal = {Journal of integer sequences},
     year = {2004},
     volume = {7},
     number = {1},
     zbl = {1069.11002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2004__7_1_a6/}
}