TY  - RPRT
TI  - Some sources of difficulty in solving simple problems.
AU  - J J GOODNOW
AU  - T F PETTIGREW
PY  - 1956
DO  - 10.1037/h0049059
UR  - https://pubmed.ncbi.nlm.nih.gov/13319610/
ID  - 13319610
ER  -