Persson, B. <br/><br/>
Experimental studies in the use of abstract and concrete concepts in problem solving / 
[by] B. Persson, I. Werdelin and Kristina Wimo. 
 - Malmo :  Dept. of Educational & Psychological Research, School of Education,  1968. 
 - Didakometry ;  no. 19 .
<br/><br/>Bibliography: p. 16-17. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Concepts.<br/>Problem solving.<br/>Abstraction.