TY  - JOUR
AU  - Jan Niechwiej
TI  - Cosine Functions of Unbounded Operators and Second Order Differential Equations
JO  - Mathematica balkanica
PY  - 1990
SP  - 329
VL  - 4
IS  - 3-4
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MABA_1990_4_3-4_a10/
ID  - MABA_1990_4_3-4_a10
ER  -