Letter to Christoffer Hansteen (1826) as quoted by Øystein Ore, Niels Henrik Abel: Mathematician Extraordinary (1957) & in part by Morris Kline, Mathematical Thought from Ancient to Modern Times (1972) citing Œuvres, 2, 263-65
Niels Henrik Abel: Frases em inglês
A Memoir on Algebraic Equations, Proving the Impossibility of a Solution of the General Equation of the Fifth Degree (1824) Tr. W. H. Langdon, as quote in A Source Book in Mathematics (1929) ed. David Eugene Smith
Letter to Bernt Michael Holmboe (ca. 1826) as quoted by Øystein Ore, Niels Henrik Abel: Mathematician Extraordinary (1957)
A Memoir on Algebraic Equations, Proving the Impossibility of a Solution of the General Equation of the Fifth Degree (1824) Tr. W. H. Langdon, as quote in A Source Book in Mathematics (1929) ed. David Eugene Smith
Marginal note in his mathematical notebook (ca. 1826) as quoted by Øystein Ore, Niels Henrik Abel: Mathematician Extraordinary (1957)
Laughter retains friends
Letter to Bernt Michael Holmboe (Jan. 1826) as quoted by Arild Stubhaug, Niels Henrik Abel and his Times: Called Too Soon by Flames Afar (2013)