Michael Haydn's Symphony No. 26 in E-flat major, Perger 17, Sherman 26, MH 340, written in Salzburg in 1783, was the first of the only three symphonies published in his lifetime. It was one of several E-flat major symphonies attributed to Joseph Haydn (Hob. I:Es17).
The first of these movements is now acknowledged by scholars to have been an important influence on Wolfgang Amadeus Mozart's Symphony No. 39, K. 543 in the same key.[1]
^Alfred Einstein, Mozart: His Character, His Work, translated to English by Arthur Mendel & Nathan Broder. Oxford: Oxford University Press (1945): 127. "But, as regards the E-flat Symphony [K. 543], it was probably the beginning of a symphony by Michael of 14 August 1783—Mozart was then in Salzburg and may have become acquainted with the work—that supplied the stimulus for the first Allegro: Ex. 7 [four bars of music are quoted in piano reduction] Similarly with the Adagio affettuoso of the Haydn work and Mozart's Andante."
A. Delarte, "A Quick Overview Of The Instrumental Music Of Michael Haydn" Bob's Poetry Magazine November 2006: 22 PDF
Charles H. Sherman and T. Donley Thomas, Johann Michael Haydn (1737 - 1806), a chronological thematic catalogue of his works. Stuyvesant, New York: Pendragon Press (1993)
C. Sherman, "Johann Michael Haydn" in The Symphony: Salzburg, Part 2 London: Garland Publishing (1982): lxviii
M. H. Schmid, liner notes to Warchal box set: 20 - 22