TY  - JOUR
AU  - A. V. Chagrov
TI  - Undecidable properties of extensions of provability logic
JO  - Algebra i logika
PY  - 1990
SP  - 350
EP  - 367
VL  - 29
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/AL_1990_29_3_a6/
LA  - ru
ID  - AL_1990_29_3_a6
ER  -