Book/Conceptual Mathematics/OnSymmetries

Lawvere, William; Schanuel, Stephen (January 8, 2009). Conceptual Mathematics_A First Introduction to Categories (2nd ed.). local page: Cambridge University Press. p. 180. ISBN 978-0521719162. 

<quote>In 1872 Felix Klein proposed that the way to study an object is to investigate all its [[wikipedia:automorphisms|automorphism]s, which he called symmetries. </quote>