Archival Sources
correspondence, manuscripts and other documents of Gösta Mittag-Leffler, Sofia Kovalevskaya and Karl Weierstrass.
See also: Joan Spicci's website for a description, summary and selected translations of Kovalevskaya's letters from the Russian edition: Reminiscences and Letters, edited by S. Ia htraikh. Moscow, Academia Nauk SSSR, 1951.