Question: Who is the father of the composer of Piano Sonata No. 9?

full_context: Document 1: Wolfgang Amadeus Mozart: Wolfgang Amadeus Mozart (/ ˈwʊlfɡæŋ æməˈdeɪəs ˈmoʊtsɑːrt / MOHT - sart; German: (ˈvɔlfɡaŋ amaˈdeːʊs ˈmoːtsaʁt); 27 January 1756 -- 5 December 1791), baptised as Johannes Chrysostomus Wolfgangus Theophilus Mozart, was a prolific and influential composer of the Classical era.
Document 2: Luigi Gatti: Luigi Gatti (October 7, 1740 – March 1, 1817) was a classical composer. He was born in Lazise in 1740, the son of an organist, Francesco della Gatta. He was ordained a priest in Mantua. In the 1780s he became Hofkapellmeister in Salzburg and Leopold Mozart showed his irritation at not receiving it himself. Between 1801 and 1804 Gatti helped Mozart's sister, Nannerl to locate unknown pieces by Mozart. He died in Salzburg in 1817.
Document 3: Piano Sonata No. 9 (Mozart): Wolfgang Amadeus Mozart's Piano Sonata No. 9 in D major, K. 311 / 284c, was written on the composer's stay in Augsburg and Mannheim in November-December 1777, and is contemporaneous with his Sonata K. 309 (Mozart wrote his Sonata K. 310 in the summer of the following year, in Paris). The three sonatas K. 309–311 were published as a set 'Opus IV' in about 1782, by Franz Joseph Heina in Paris.
Document 4: Piano Sonata No. 6 (Mozart): Wolfgang Amadeus Mozart's Piano Sonata No. 6 in D major, K. 284 / 205b, (1775) is a sonata in three movements:
Document 5: Joseph Lange: Joseph Lange (Würzburg, 1 April 1751 – Vienna, 17 September 1831) was an actor and amateur painter of the 18th century. Through his marriage to Aloysia Weber, he was the brother-in-law of Wolfgang Amadeus Mozart.
Document 6: Franz Xaver Wolfgang Mozart: Franz Xaver Wolfgang Mozart (26 July 1791 – 29 July 1844), also known as Wolfgang Amadeus Mozart, Jr., was the youngest child of six born to Wolfgang Amadeus Mozart and his wife Constanze. He was the younger of his parents' two surviving children. He was a composer, pianist, conductor, and teacher from the late classical period whose musical style was of an early Romanticism, heavily influenced by his father's mature style.
Document 7: Mozart's birthplace: Mozart's birthplace (German: ' or ') was the birthplace of Wolfgang Amadeus Mozart at No. 9 Getreidegasse in Salzburg, Austria. The Mozart family resided on the third floor from 1747 to 1773. Mozart himself was born here on 27 January 1756. He was the seventh child of Leopold Mozart, who was a musician of the Salzburg Royal Chamber.
Document 8: Piano Sonata No. 7 (Mozart): The work was composed during a journey to Mannheim and Paris in 1777-78. The sonata was completed in a few days in early November 1777. The andante movement is a "portrait" of his pupil Rose Cannabich, the 13-year-old daughter of the Mannheim Kapellmeister Christian Cannabich. Upon reviewing a copy of the manuscript, Mozart's father Leopold wrote that it was "a strange composition. It has something in it of the 'rather artificial' Mannheim style, but so very little that your own good style is not spoilt".
Document 9: Piano Sonata No. 8 (Mozart): Wolfgang Amadeus Mozart's Piano Sonata No. 8 in A minor, K. 310 / 300d, was written in 1778. The sonata is the first of only two Mozart piano sonatas in a minor key (the other being No. 14 in C minor, K. 457). It was composed in the summer of 1778 around the time of his mother's death, one of the most tragic times of his life.
Document 10: Symphony, K. 45b (Mozart): This work was only known to Ludwig Ritter von Köchel as an incipit in the catalogue of Breitkopf & Härtel, and thus it was placed in the Anhang as K. Anh. 214. Alfred Einstein then discovered a set of parts in the Berlin State Library with the title ""Synfonia Ex Bb...Del Sigr. cavaliere Amadeo Wolfgango Mozart Maestro di concerto di S.A. á Salisburgo"". Wolfgang became the Concertmaster to the Archbishop of Salzburg in November 1769, and was given the title "cavaliere" in July 1770, but as this is a later copy, this information cannot be used for dating purposes. Einstein believed the symphony to date from early 1768 on stylistic grounds; Neal Zaslaw and Gerhard Allroggen believe even earlier dates to also be possible, and Zaslaw dated the symphony cautiously to Salzburg in 1767. Einstein also believed that the symphonies in the catalogue of Breitkopf & Härtel were sent by Leopold Mozart to be published.
Document 11: Piano Sonata No. 1 (Mozart): Wolfgang Amadeus Mozart's Piano Sonata No. 1 in C major, K. 279 / 189d (1774), is a piano sonata in three movements. It was written down, except for the first part of the opening movement, during the visit Mozart paid to Munich for the production of "La finta giardiniera" from late 1774 to the beginning of the following March. A typical performance of the sonata takes about 14 minutes. It is the first of his 18 piano sonatas. All but two of the sonatas, No. 8 in A minor and No. 14 in C minor, are in a major key. Also, the first six sonatas seem to follow the cycle of fifths, to the flat side first (No. 1 in C major, No. 2 in F major, No. 3 in B-flat major, No. 4 in E-flat major) and then to the sharp side (No. 5 in G major, No. 6 in D major).
Document 12: Wolfgang Amadeus Mozart: Wolfgang Amadeus Mozart was born on 27January 1756 to Leopold Mozart (1719–1787) and Anna Maria, née Pertl (1720–1778), at 9 Getreidegasse in Salzburg. This was the capital of the Archbishopric of Salzburg, an ecclesiastic principality in what is now Austria, then part of the Holy Roman Empire. He was the youngest of seven children, five of whom died in infancy. His elder sister was Maria Anna Mozart (1751–1829), nicknamed "Nannerl". Mozart was baptised the day after his birth, at St. Rupert's Cathedral in Salzburg. The baptismal record gives his name in Latinized form, as "Joannes Chrysostomus Wolfgangus Theophilus Mozart". He generally called himself "Wolfgang Amadè Mozart" as an adult, but his name had many variants.
Document 13: Piano Concertos Nos. 1–4 (Mozart): Wolfgang Amadeus Mozart began his series of preserved piano concertos with four that he wrote at the age of 11, in Salzburg: K. 37 and 39–41. The autographs, all held by the Jagiellonian Library, Kraków, are dated by his father as having been completed in April (K. 37) and July (K. 39–41) of 1767. Although these works were long considered to be original, they are now known to be orchestrations of sonatas by various German virtuosi. The works on which the concertos are based were largely published in Paris, and presumably Mozart and his family became acquainted with them or their composers during their visit to Paris in 1763–64.
Document 14: Biographies of Mozart: Wolfgang Amadeus Mozart died after a short illness on 5 December 1791, aged 35. His reputation as a composer, already strong during his lifetime, rose rapidly in the years after his death, and he became (as he has remained to this day) one of the most celebrated of all composers.
Document 15: Piano Sonata No. 17 (Mozart): Wolfgang Amadeus Mozart's Piano Sonata No. 17 in B major, K. 570, dated February 1789, is a sonata in three movements:
ground_truth: Leopold Mozart
sub_queries: Piano Sonata No. 9 >> composer Answer: Wolfgang Amadeus Mozart
Who was the dad of Wolfgang Amadeus Mozart ? Answer: Leopold Mozart