Harsh Gupta. (2017, February 11). How High Can You Count On Your Fingers? . Retrieved April 28, 2018, From https://www.scienceabc.com/pure-sciences/high-can-count-fingers.html
James Tanton. (2016, December 15). How high can you count on your fingers? (Spoiler: much higher than 10). Retrieved April 28, 2018, From https://ed.ted.com/lessons/how-high-can-you-count-on-your-fingers-spoiler-much-higher-than-10-james-tanton
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