Question: Who was mentored by Arnold Schoenberg and worked on the album "At the Grave of Richard Wagner"?

Context paragraphs:
Arnold Schoenberg Choir: The Arnold Schoenberg Choir (German: "Arnold Schoenberg Chor" ) is a Viennese/Austrian choir which was founded 1972 by Erwin Ortner, who is still its artistic director.  The choir has a high reputation both among conductors and among critics and the musical scene in general.  All members of the choir have broad experience and expertise in vocal music; most of them have graduated from or are currently studying at the Vienna University of Music and Performing Arts.  The choir is named after Viennese composer Arnold Schoenberg.

At the Grave of Richard Wagner: At the Grave of Richard Wagner is a studio album by the Kronos Quartet, containing works by Alban Berg and Anton Webern, and a brief "romantic elegy" by Franz Liszt.

Die Jakobsleiter: Die Jakobsleiter ("Jacob's Ladder") is an oratorio by Arnold Schoenberg that marks his transition from a contextual or free atonality to the twelve-tone technique anticipated in the oratorio's use of hexachords. Though ultimately unfinished by Schoenberg the piece was prepared for performance by Schoenberg student Winfried Zillig at the request of Gertrude Schoenberg.

Moses und Aron: Moses und Aron (English: "Moses and Aaron") is a three-act opera by Arnold Schoenberg with the third act unfinished.  The German libretto is by the composer after the Book of Exodus.  Hungarian composer Zoltán Kocsis completed the last act, with Schoenberg's heirs' permission, in 2010, but as of 2014 "Moses und Aron" was almost always performed as Schoenberg left it in 1932, with only two of the planned three acts completed.

Second Viennese School: The Second Viennese School (German: Zweite Wiener Schule, Neue Wiener Schule ) is the group of composers that comprised Arnold Schoenberg and his pupils and close associates in early 20th century Vienna, where he lived and taught, sporadically, between 1903 and 1925.  Their music was initially characterized by late-Romantic expanded tonality and later, following Schoenberg's own evolution, a totally chromatic expressionism without firm tonal centre, often referred to as atonality; and later still, Schoenberg's serial twelve-tone technique.  Though this common development took place, it neither followed a common time-line nor a cooperative path.  Likewise, it was not a direct result of Schoenberg's teaching—which, as his various published textbooks demonstrate, was highly traditional and conservative.  Schoenberg's textbooks also reveal that the Second Viennese School spawned not from the development of his serial method, but rather from the influence of his creative example.

Style and Idea (Schoenberg): Style and Idea: Selected Writings of Arnold Schoenberg (in German: "Stil und Gedanke") is the name for a published collection of essays, articles and sketches by Arnold Schoenberg, that has appeared in various forms.

Anton Webern: Anton Friedrich Wilhelm (von) Webern (] ; 3 December 188315 September 1945) was an Austrian composer and conductor.  Along with his mentor Arnold Schoenberg and his colleague Alban Berg, Webern was at the core among those within and more peripheral to the circle of the Second Viennese School, including Ernst Krenek and Theodor W. Adorno.  As an exponent of atonality and twelve-tone technique, Webern exerted influence on contemporaries Luigi Dallapiccola, Křenek, and even Schoenberg himself.  As a tutor, Webern guided and variously influenced Arnold Elston, Frederick Dorian (Friederich Deutsch), Matty Niël, Fré Focke, Karl Amadeus Hartmann, Philipp Herschkowitz, René Leibowitz, Humphrey Searle, Leopold Spinner, and Stefan Wolpe.

Schoenberg hexachord: 6-Z44 (012569), known as the Schoenberg hexachord, is Arnold Schoenberg's signature hexachord, as one transposition contains the pitches [A], Es, C, H, B, E, G (A. Schoenberg), E♭ , B, and B♭ being Es, H, and B in German.

Die glückliche Hand: Die glückliche Hand ("The Hand of Fate"), Op.  18, is a "Drama mit Musik" ("drama with music") by Arnold Schoenberg in four scenes.  It was composed between 1910 and 1913.  Like "Erwartung", composed a year earlier, it was heavily influenced by Otto Weininger's book "Sex and Character".  Unlike "Erwartung", Schoenberg wrote the libretto for "Die glückliche Hand" himself.  The first performance took place in Vienna on 24 October 1924.  The underlying message of the piece is the idea that man continues to repeatedly make the same mistakes, and the plot is developed from events in Schoenberg’s personal life.

Seven Early Songs (Berg): The Seven Early Songs ("Sieben frühe Lieder") (c. 1905 – 1908), are early compositions of Alban Berg, written while he was under the tutelage of Arnold Schoenberg.  They are an interesting synthesis combining Berg's heritage of pre-Schoenberg song writing with the rigour and undeniable influence of Schoenberg.  The writing very much carries with it the heritage of Richard Strauss (although the influences of a number of other composers can be discerned – Gustav Mahler and Hugo Wolf for example, as well as Claude Debussy's harmonic palette in evidence in "Nacht"), through the expansiveness of gesture and 'opening of new vistas,' and that of Richard Wagner.  The songs were first written for a medium voice and piano; they were revised for high voice and orchestra in 1928.

Supporting paragraphs: At the Grave of Richard Wagner Anton Webern
Answer: Anton Webern