TY  - BOOK
AU  - Sigel,Irving E
AU  - Hooper,Frank H
TI  - Logical thinking in children: research based on Piaget's theory 
U1  - 136.5 
PY  - 1968///
CY  - New York
PB  - Holt, Rinehart and Winston
KW  - Piaget, Jean,
KW  - Conservation of substance (Psychology)
KW  - Child psychology
N1  - Includes index
ER  -