TY  - BOOK
AU  - Popkorn, Sally
TI  - First steps in modal logic
SN  - 9780521057936
U1  - 511.3 POP 
PY  - 1994///
CY  - Cambridge
PB  - Cambridge University Press
KW  - Modality (Logic)
N1  - Includes bibliographical references (p. 311-314)
ER  -