TY  - BOOK
AU  - Prawitz, Dag
TI  - Natural deduction: A proof theoretical study 
SN  - 9780486446554
U1  - 510 
PY  - 1965///
CY  - New  York
PB  - Dover Publications
KW  - Deduction
KW  - Symbolic and mathematical
KW  - Modality
KW  - Logic
ER  -