TY  - BOOK
AU  - Sigel,Irving E
AU  - Hooper,Frank H.
AU  - Piaget,Jean
TI  - Logical thinking in children; research based on Piaget's theory
U1  - 155.4 
PY  - 1968///
CY  - New York
PB  - Holt, Rinehart and Winston
KW  - Conservation of substance (Psychology)
KW  - Child psychology
N1  - Includes bibliographies
ER  -