@article{VMUMM_1996_1_a1,
     author = {R. \`E. Yavorskii},
     title = {Axiom systems and models for first-order theories with a provability operator},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {12--16},
     year = {1996},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1996_1_a1/}
}