Lachaud, Gilles (29 January 2025). "Équation, mathématique". Encyclopædia Universalis (in French).
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de.wikipedia.org
"A statement of equality between two expressions. Equations are of two types, identities and conditional equations (or usually simply "equations")". « Equation », in Mathematics Dictionary, Glenn James [de] et Robert C. James (éd.), Van Nostrand, 1968, 3 ed. 1st ed. 1948, p. 131.