Number line (English Wikipedia)

Núñez, Rafael (2017). "How Much Mathematics Is 'Hardwired', If Any at All: Biological Evolution, Development, and the Essential Role of Culture". Maria D. Sera, Michael Maratsos and Stephanie M. Carlson (2017). Minnesota Symposia on Child Psychology: Culture and Developmental Systems, Volume 38: Culture and Developmental Systems. Hoboken, NJ: John Wiley & Sons. p. 98. ISBN 9781119247654. OCLC 961910599.
Introduction to the x,y-plane (Archived 2015-11-09 at the Wayback Machineº "Purplemath" Retrieved 2015-11-13.

worldcat.org (Global: 4^th place; English: 4^th place)

Núñez, Rafael (2017). "How Much Mathematics Is 'Hardwired', If Any at All: Biological Evolution, Development, and the Essential Role of Culture". Maria D. Sera, Michael Maratsos and Stephanie M. Carlson (2017). Minnesota Symposia on Child Psychology: Culture and Developmental Systems, Volume 38: Culture and Developmental Systems. Hoboken, NJ: John Wiley & Sons. p. 98. ISBN 9781119247654. OCLC 961910599.