@article{10_4064_fm_43_1_36_45,
     author = {S. Ja\'skowski},
     title = {Undecidability of first order sentences in the theory of free groupoids},
     journal = {Fundamenta Mathematicae},
     pages = {36--45},
     publisher = {mathdoc},
     volume = {43},
     number = {1},
     year = {1956},
     doi = {10.4064/fm-43-1-36-45},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-43-1-36-45/}
}