Editing Maurice Ravel (section)

==Music==
{{see also|List of compositions by Maurice Ravel}}
[[Marcel Marnat]]'s catalogue of Ravel's complete works lists eighty-five works, including many incomplete or abandoned.<ref name=marnat>Marnat, pp. 721–784</ref> Though that total is small in comparison with the output of his major contemporaries,{{refn|''[[Grove's Dictionary of Music and Musicians]]'' credits Saint-Saëns with 169 works, Fauré with 121 works and Debussy with 182.<ref>[[Jean-Michel Nectoux|Nectoux Jean-Michel]]. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/09366 "Fauré, Gabriel] {{Webarchive|url=https://web.archive.org/web/20200530041625/https://www.oxfordmusiconline.com/grovemusic/view/10.1093/gmo/9781561592630.001.0001/omo-9781561592630-e-0000009366 |date=30 May 2020 }}"; Ratner, Sabina Teller, et al. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/24335 "Saint-Saëns, Camille"]; and [[Lesure, François]] and [[Roy Howat]]. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/07353. "Debussy, Claude"], ''Grove Music Online'', Oxford University Press, retrieved 13 March 2015 {{subscription}}</ref>|group= n}} it is nevertheless inflated by Ravel's frequent practice of writing works for piano and later rewriting them as independent pieces for orchestra.<ref name=rg/> The performable body of works numbers about sixty; slightly more than half are instrumental. Ravel's music includes pieces for piano, chamber music, two piano concerti, ballet music, opera and song cycles. He wrote no symphonies or church works.<ref name=marnat/>

Ravel drew on many generations of French composers from Couperin and [[Rameau]] to Fauré and the more recent innovations of Satie and Debussy. Foreign influences include Mozart, [[Schubert]], [[Liszt]] and Chopin.<ref>Orenstein (1991), pp. 64 (Satie), 123 (Mozart and Schubert), 124 (Chopin and Liszt), 136 (Russians), 155 (Debussy) and 218 (Couperin and Rameau)</ref> He considered himself in many ways a [[classicism|classicist]], often using traditional structures and forms, such as the [[ternary form|ternary]], to present his new melodic and rhythmic content and innovative harmonies.<ref>Orenstein (1991), p. 135</ref> The influence of jazz on his later music is heard within conventional classical structures in the Piano Concerto and the Violin Sonata.<ref>Nichols (2011), pp. 291, 314 and 319</ref>

{{Quote box|width=33%|bgcolor=#c6dbf7|align=right|quoted=y | quote= Whatever sauce you put around the melody is a matter of taste. What is important is the melodic line.|salign = right|source=Ravel to Vaughan Williams<ref>''Quoted'' in Orenstein (1991), p. 131</ref>}}
Ravel placed high importance on melody, telling Vaughan Williams that there is "an implied melodic outline in all vital music".<ref>Orenstein (1991), p. 131</ref> His themes are frequently [[mode (music)|modal]], eschewing the familiar major or minor scales.<ref>Taruskin, p. 112; and [http://www.oxfordmusiconline.com/subscriber/article/grove/music/16179 "Leading note"], ''Grove Music Online'', Oxford University Press, retrieved 13 March 2015 {{subscription}}</ref> Chords of the [[extended chord|ninth and eleventh]] and unresolved [[appoggiatura]]s, such as those in the ''Valses nobles et sentimentales'', are characteristic of Ravel's harmonic language.<ref>Orenstein (1991), p. 132</ref>

Dance forms appealed to Ravel, most famously the [[bolero]] and pavane, but also the [[minuet]], [[forlane]], [[rigaudon]], [[Waltz (music)|waltz]], [[czardas]], [[Habanera (music)|habanera]] and [[passacaglia]]. National and regional consciousness was important to him, and although a planned concerto on Basque themes never materialised, his works include allusions to [[Hebraic]], [[Greek language|Greek]], [[Hungarian language|Hungarian]] and [[gypsy]] themes.<ref>Orenstein (1991), pp. 190 and 193</ref> He wrote several short pieces paying tribute to composers he admired – [[Borodin]], Chabrier, Fauré and [[Haydn]], interpreting their characteristics in a Ravellian style.<ref>Orenstein (1991), p. 192</ref> Another important influence was literary rather than musical: Ravel said that he learnt from Poe that "true art is a perfect balance between pure intellect and emotion",<ref>Lanford, pp. 245–246</ref> with the corollary that a piece of music should be a perfectly balanced entity with no irrelevant material allowed to intrude.<ref>Lanford, pp. 248–249.</ref>

===Operas===
[[File:L'heure-espagnole-1911.jpg|thumb|upright|alt=pencil sketches of characters in comic opera, head and shoulders only|Sketches of the cast for the 1911 premiere of ''[[L'heure espagnole]]'' by {{ill|Paul-Charles Delaroche|fr}}]]
Ravel completed two operas, and worked on three others. The unrealised three were ''Olympia'', ''La cloche engloutie'' and ''Jeanne d'Arc''. ''Olympia'' was to be based on [[E. T. A. Hoffmann|Hoffmann]]'s ''The Sandman''; he made sketches for it in 1898–99, but did not progress far. ''La cloche engloutie'' after [[Gerhart Hauptmann|Hauptmann]]'s ''[[The Sunken Bell]]'' occupied him intermittently from 1906 to 1912, Ravel destroyed the sketches for both these works, except for a ''"Symphonie horlogère"'' which he incorporated into the opening of ''L'heure espagnole''.<ref>Zank, pp. 105 and 367</ref> The third unrealised project was an operatic version of [[Joseph Delteil]]'s 1925 novel about [[Joan of Arc]]. It was to be a large-scale, full-length work for the Paris Opéra, but Ravel's final illness prevented him from writing it.<ref>Nichols (1987), pp. 171–172</ref>

Ravel's first completed opera was ''L'heure espagnole'' (premiered in 1911), described as a "comédie musicale".<ref name=grove-heure/> It is among the works set in or illustrating Spain that Ravel wrote throughout his career. Nichols comments that the essential Spanish colouring gave Ravel a reason for virtuoso use of the modern orchestra, which the composer considered "perfectly designed for underlining and exaggerating comic effects".<ref>Nichols (2011), p. 129</ref> [[Edward Burlingame Hill]] found Ravel's vocal writing particularly skilful in the work, "giving the singers something besides recitative without hampering the action", and "commenting orchestrally upon the dramatic situations and the sentiments of the actors without diverting attention from the stage".<ref>Hill, p. 144</ref> Some find the characters artificial and the piece lacking in humanity.<ref name=grove-heure>Nichols, Roger. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/O002204 "Heure espagnole, L'"] {{Webarchive|url=https://web.archive.org/web/20210316071721/https://www.oxfordmusiconline.com/view/10.1093/gmo/9781561592630.001.0001/omo-9781561592630-e-5000002204;jsessionid=112DA8BB98B87C022CB0A459D6633BF0 |date=16 March 2021 }}, ''The New Grove Dictionary of Opera'', Oxford Music Online, Oxford University Press, retrieved 14 March 2015 {{subscription}}</ref> The critic David Murray writes that the score "glows with the famous Ravel ''tendresse''."<ref>Murray, p. 316</ref>

The second opera, also in one act, is ''[[L'enfant et les sortilèges]]'' (1926), a "fantaisie lyrique" to a libretto by Colette. She and Ravel had planned the story as a ballet, but at the composer's suggestion Colette turned it into an opera libretto. It is more uncompromisingly modern in its musical style than ''L'heure espagnole'', and the jazz elements and [[bitonality]] of much of the work upset many Parisian opera-goers. Ravel was once again accused of artificiality and lack of human emotion, but Nichols finds "profoundly serious feeling at the heart of this vivid and entertaining work".<ref>Nichols, Roger. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/O003509 "Enfant et les sortilèges, L'"] {{Webarchive|url=https://web.archive.org/web/20210316071720/https://www.oxfordmusiconline.com/view/10.1093/gmo/9781561592630.001.0001/omo-9781561592630-e-5000003509;jsessionid=59A9AA4CF097ACC4239F1ADE1D30D6E9 |date=16 March 2021 }}, ''The New Grove Dictionary of Opera'', Oxford Music Online, Oxford University Press, retrieved 14 March 2015 {{subscription}}</ref> The score presents an impression of simplicity, disguising intricate links between themes, with, in Murray's phrase, "extraordinary and bewitching sounds from the orchestra pit throughout".<ref>Murray, p. 317</ref>

Although one-act operas are generally staged less often than full-length ones,<ref>White, p. 306</ref> Ravel's are produced regularly in France and abroad.<ref>[https://www.operabase.com/productions/en?date_from=2010-01-01&date_to=2023-06-19&aggregation_query=&is_producer_approved=true&approved_by=admin%2Ccompany%2Cfestival&work_creator_id=2152463 "Maurice Ravel"], [[Operabase]], performances since 2010.</ref>

===Other vocal works===
A substantial proportion of Ravel's output was vocal. His early works in that sphere include cantatas written for his unsuccessful attempts at the Prix de Rome. His other vocal music from that period shows Debussy's influence, in what Kelly describes as "a static, recitative-like vocal style", prominent piano parts and rhythmic flexibility.<ref name=grove/> By 1906 Ravel was taking even further than Debussy the natural, sometimes colloquial, setting of the French language in ''Histoires naturelles''. The same technique is highlighted in ''[[Trois poèmes de Mallarmé]]'' (1913); Debussy set two of the three poems at the same time as Ravel, and the former's word-setting is noticeably more formal than the latter's, in which syllables are often elided. In the cycles ''Shéhérazade'' and ''Chansons madécasses'', Ravel gives vent to his taste for the exotic, even the sensual, in both the vocal line and the accompaniment.<ref name=grove/><ref>Orenstein (1991), p. 157</ref>

Ravel's songs often draw on vernacular styles, using elements of many folk traditions in such works as ''Cinq mélodies populaires grecques'', ''[[Deux mélodies hébraïques]]'' and ''Chants populaires''.<ref>Jankélévitch, pp. 29–32</ref> Among the poets on whose lyrics he drew were Marot, [[Léon-Paul Fargue]], [[Leconte de Lisle]] and Verlaine. For three songs dating from 1914 to 1915, he wrote his own texts.<ref>Jankélévitch, p. 177</ref>

Although Ravel wrote for mixed choirs and male solo voices, he is chiefly associated, in his songs, with the soprano and mezzo-soprano voices. Even when setting lyrics clearly narrated by a man, he often favoured a female voice,<ref>Nichols (2011), p. 280</ref> and he seems to have preferred his best-known cycle, ''Shéhérazade'', to be sung by a woman, although a tenor voice is a permitted alternative in the score.<ref>Nichols (2011), p. 55</ref>

===Orchestral works===
During his lifetime it was above all as a master of orchestration that Ravel was famous.<ref>Goddard, p. 291</ref> He minutely studied the ability of each orchestral instrument to determine its potential, putting its individual colour and timbre to maximum use.<ref>James, p. 21</ref> The critic [[Alexis Roland-Manuel]] wrote, "In reality he is, with Stravinsky, the one man in the world who best knows the weight of a trombone-note, the harmonics of a 'cello or a ''pp'' [[tam-tam]] in the relationships of one orchestral group to another."<ref>''Quoted'' in Goddard, p. 292</ref>

[[File:Bakst Daphnis et Chloë Set Act II 1912.jpg|thumb|left|alt=rustic-looking stage scenery depicting an ancient bower|Original setting for ''[[Daphnis et Chloé]]'' by [[Léon Bakst]] (1912)]]
For all Ravel's orchestral mastery, only four of his works were conceived as concert works for symphony orchestra: ''Rapsodie espagnole'', ''La valse'' and the two concertos. All the other orchestral works were written either for the stage, as in ''Daphnis et Chloé'', or as a reworking of piano pieces, ''Alborada del gracioso'' and ''Une barque sur l'ocean'', (''Miroirs''), ''Valses nobles et sentimentales,'' ''Ma mère l'Oye'', ''Tzigane'' (originally for violin and piano) and ''Le tombeau de Couperin.''<ref>Sackville-West and Shawe-Taylor, pp. 611–612; and Goddard, p. 292</ref> In the orchestral versions, the instrumentation generally clarifies the harmonic language of the score and brings sharpness to classical dance rhythms.<ref>Goddard, pp. 293–294</ref> Occasionally, as in the ''Alborada del gracioso'', critics have found the later orchestral version less persuasive than the sharp-edged piano original.<ref>Sackville-West and Shawe-Taylor, p. 611</ref>

In some of his scores from the 1920s, including ''Daphnis et Chloé'', Ravel frequently divides his upper strings, having them play in six to eight parts while the woodwind are required to play with extreme agility. His writing for the brass ranges from softly muted to triple-forte outbursts at climactic points.<ref>Goddard, pp. 298–301</ref> In the 1930s he tended to simplify his orchestral textures. The lighter tone of the G major Piano Concerto follows the models of [[Mozart]] and Saint-Saëns, alongside use of jazz-like themes.<ref>Orenstein (1991), pp. 204–205</ref> The critics [[Edward Sackville-West]] and [[Desmond Shawe-Taylor (music critic)|Desmond Shawe-Taylor]] comment that in the slow movement, "one of the most beautiful tunes Ravel ever invented", the composer "can truly be said to join hands with Mozart".<ref>Sackville-West and Shawe-Taylor, p. 610</ref> The most popular of Ravel's orchestral works, ''[[Boléro]]'' (1928), was conceived several years before its completion; in 1924 he said that he was contemplating "a symphonic poem without a subject, where the whole interest will be in the rhythm".<ref>Nichols (2011), p. 302</ref>

Ravel made orchestral versions of piano works by Schumann, Chabrier, Debussy and Mussorgsky's piano suite ''Pictures at an Exhibition''. Orchestral versions of the last by [[Mikhail Tushmalov]], [[Sir Henry Wood]] and [[Leo Funtek]] predated Ravel's 1922 version, and many more have been made since, but Ravel's remains the best known.<ref>Oldani, Robert W. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/19468 "Musorgsky, Modest Petrovich"], ''Grove Music Online'', Oxford University Press, retrieved 16 March 2015 {{subscription}}</ref> Kelly remarks on its "dazzling array of instrumental colour",<ref name=grove/> and a contemporary reviewer commented on how, in dealing with another composer's music, Ravel had produced an orchestral sound wholly unlike his own.<ref>Nichols (2011), p. 248</ref>

===Piano music===
Although Ravel wrote fewer than thirty works for the piano, they exemplify his range; Orenstein remarks that the composer keeps his personal touch "from the striking simplicity of ''Ma mère l'Oye'' to the transcendental virtuosity of ''Gaspard de la nuit''".<ref>Orenstein (1991), p. 193</ref> Ravel's earliest major work for piano, ''Jeux d'eau'' (1901), is frequently cited as evidence that he evolved his style independently of Debussy, whose major works for piano all came later.<ref>Orenstein (1981), p. 32; and Sackville-West and Shawe-Taylor, p. 613</ref> When writing for solo piano, Ravel rarely aimed at the intimate chamber effect characteristic of Debussy, but sought a Lisztian virtuosity.<ref name=s613/> The authors of ''The Record Guide'' consider that works such as ''Gaspard de la Nuit'' and ''Miroirs'' have a beauty and originality with a deeper inspiration "in the harmonic and melodic genius of Ravel himself".<ref name=s613>Sackville-West and Shawe-Taylor, p. 613</ref>

{{Listen
|type=music
|title=Pavane pour une infante défunte
|filename=Maurice Ravel - Thérèse Dussaut - Pavane pour une infante défunte.ogg
|description=Performed by [[Thérèse Dussaut]]
}}
Most of Ravel's piano music is extremely difficult to play, and presents pianists with a balance of technical and artistic challenges.<ref>Sackville-West and Shawe-Taylor, pp. 613–614</ref>{{refn|In 2009 the pianist [[Steven Osborne (pianist)|Steven Osborne]] wrote of ''Gaspard'', "This bloody opening! I feel I've tried every possible fingering and nothing works. In desperation, I divide the notes of the first bar between my two hands rather than playing them with just one, and suddenly I see a way forward. But now I need a third hand for the melody."<ref>Osborne, Steven. [https://www.theguardian.com/music/2011/sep/29/steven-osborne-diary-ravel "Wrestling with Ravel : How do you get your fingers – and brain – round one of the most difficult pieces in the piano repertoire?"], ''The Guardian'', 30 September 2011</ref>|group= n}} Writing of the piano music the critic Andrew Clark commented in 2013, "A successful Ravel interpretation is a finely balanced thing. It involves subtle musicianship, a feeling for pianistic colour and the sort of lightly worn virtuosity that masks the advanced technical challenges he makes in ''Alborada del gracioso''{{nbsp}}... and the two outer movements of ''Gaspard de la nuit''. Too much temperament, and the music loses its classical shape; too little, and it sounds pale."<ref name=clark>Clark, Andrew. [http://www.ft.com/cms/s/2/07a830e6-5fe1-11e2-8d8d-00144feab49a.html#axzz3Vwt4Lc3k "All the best: Ravel's piano music"] {{Webarchive|url=https://web.archive.org/web/20150402095821/http://www.ft.com/cms/s/2/07a830e6-5fe1-11e2-8d8d-00144feab49a.html#axzz3Vwt4Lc3k |date=2 April 2015 }}, ''The Financial Times'', 16 January 2013</ref> This balance caused a breach between the composer and Viñes, who said that if he observed the nuances and speeds Ravel stipulated in ''Gaspard de la nuit'', "Le gibet" would "bore the audience to death".<ref>Nichols (2011), p. 102</ref> Some pianists continue to attract criticism for over-interpreting Ravel's piano writing.<ref name=ac>Clements, Andrew. [https://www.theguardian.com/lifeandstyle/2001/oct/26/shopping.artsfeatures3 "Ravel: Gaspard de la Nuit"] {{Webarchive|url=https://web.archive.org/web/20170317083802/https://www.theguardian.com/lifeandstyle/2001/oct/26/shopping.artsfeatures3 |date=17 March 2017 }}, ''The Guardian'', 26 October 2001</ref>{{refn|In a 2001 survey of recordings of ''Gaspard de la nuit'' the critic Andrew Clements wrote, "[[Ivo Pogorelich]]{{nbsp}}... deserves to be on that list too, but his phrasing is so indulgent that in the end it cannot be taken seriously{{nbsp}}... Ravel's writing is so minutely calculated and carefully defined that he leaves interpreters little room for manoeuvre; [[Vladimir Ashkenazy|Ashkenazy]] takes a few liberties, so too does [[Martha Argerich|Argerich]]."<ref name=ac/> Ravel himself admonished Marguerite Long, "You should not interpret my music: you should realise it." ("Il ne faut pas interpreter ma music, il faut le réaliser.")<ref>Schuller, pp. 7–8</ref>|group= n}}

Ravel's regard for his predecessors is heard in several of his piano works; ''Menuet sur le nom de Haydn'' (1909), ''À la manière de Borodine'' (1912), ''À la manière de Chabrier'' (1913) and ''Le tombeau de Couperin'' all incorporate elements of the named composers interpreted in a characteristically Ravellian manner.<ref>Orenstein (1991), p. 181</ref> Clark comments that those piano works which Ravel later orchestrated are overshadowed by the revised versions: "Listen to ''Le tombeau de Couperin'' and the complete ballet music for ''Ma mère L'Oye'' in the classic recordings conducted by [[André Cluytens]], and the piano versions never sound quite the same again."<ref name=clark/>

===Chamber music===
Apart from a one-movement [[Violin Sonata No. 1 (Ravel)|Sonata for Violin and Piano]] dating from 1899, unpublished in the composer's lifetime, Ravel wrote seven chamber works.<ref name=grove/> The earliest is the String Quartet (1902–03), dedicated to Fauré, and showing the influence of Debussy's quartet of ten years earlier. Like the Debussy, it differs from the more monumental quartets of the established French school of Franck and his followers, with more succinct melodies, fluently interchanged, in flexible tempos and varieties of instrumental colour.<ref>Griffiths, Paul. [http://www.oxfordmusiconline.com/subscriber/article/grove/music/40899 "String quartet"], ''Grove Music Online'', Oxford University Press, retrieved 31 March 2015 {{subscription}}</ref> The [[Introduction and Allegro (Ravel)|Introduction and Allegro for harp, flute, clarinet and string quartet]] (1905) was composed very quickly by Ravel's standards. It is an ethereal piece in the vein of the ''[[Pavane pour une infante défunte]]''.<ref>Anderson (1989), p. 4</ref> Ravel also worked at unusual speed on the Piano Trio (1914) to complete it before joining the French Army. It contains Basque, Baroque and far Eastern influences, and shows Ravel's growing technical skill, dealing with the difficulties of balancing the percussive piano with the sustained sound of the violin and cello, "blending the two disparate elements in a musical language that is unmistakably his own," in the words of the commentator Keith Anderson.<ref>Anderson (1994), p. 5</ref>

Ravel's four chamber works composed after the First World War are the [[Sonata for Violin and Cello (Ravel)|Sonata for Violin and Cello]] (1920–22), the "Berceuse sur le nom de Gabriel Fauré" for violin and piano (1922), the chamber original of ''Tzigane'' for violin and piano (1924) and finally the Violin Sonata (1923–27).<ref name=grove/> The two middle works are respectively an affectionate tribute to Ravel's teacher,<ref>Phillips, p. 163</ref> and a virtuoso display piece for the violinist [[Jelly d'Arányi]].<ref>Orenstein (1991), p. 88</ref> The Violin and Cello Sonata is a departure from the rich textures and harmonies of the pre-war Piano Trio: the composer said that it marked a turning point in his career, with thinness of texture pushed to the extreme and harmonic charm renounced in favour of pure melody.<ref name=o32>Orenstein (2003), p. 32</ref> His last chamber work, the Violin Sonata (sometimes called the Second after the posthumous publication of his student sonata), is a frequently [[dissonant]] work. Ravel said that the violin and piano are "essentially incompatible" instruments, and that his Sonata reveals their incompatibility.<ref name=o32/> Sackville-West and Shawe-Taylor consider the post-war sonatas "rather laboured and unsatisfactory",<ref>Sackville-West and Shawe-Taylor, p. 612</ref> and neither work has matched the popularity of Ravel's pre-war chamber works.<ref>De Voto, p. 113</ref>

===Recordings===
Ravel's interpretations of some of his piano works were captured on [[piano roll]] between 1914 and 1928, although some rolls supposedly played by him may have been made under his supervision by [[Robert Casadesus]], a better pianist.<ref name=o532>Orenstein (2003) pp. 532–533</ref> Transfers of the rolls have been released on compact disc.<ref name=o532/> In 1913 there was a gramophone recording of ''Jeux d'eau'' played by [[Mark Hambourg]], and by the early 1920s there were discs featuring the ''Pavane pour une infante défunte'' and ''Ondine'', and movements from the String Quartet, ''Le tombeau de Couperin'' and ''Ma mère l'Oye''.<ref name=charm>[http://www.charm.rhul.ac.uk/discography/search/disco_search.html "Ravel"] {{Webarchive|url=https://web.archive.org/web/20150416160324/http://www.charm.rhul.ac.uk/discography/search/disco_search.html |date=16 April 2015 }}, Discography search, AHRC Research Centre for the History and Analysis of Recorded Music, retrieved 15 March 2015</ref> Ravel was among the first composers who recognised the potential of recording to bring their music to a wider public,{{refn|Other composers who made recordings of their music during the early years of the gramophone included [[Elgar]], [[Grieg]], [[Rachmaninoff]] and [[Richard Strauss]].<ref>Kennedy, Michael (ed). [http://www.oxfordmusiconline.com/subscriber/article/opr/t237/e4435 "Gramophone (Phonograph) Recordings"], The Oxford Dictionary of Music, Oxford University Press, retrieved 6 April 2015 {{subscription}}</ref>|group= n}} and throughout the 1920s there was a steady stream of recordings of his works, some of which featured the composer as pianist or conductor.<ref>''The Gramophone'', Volume I, pp. 60, 183, 159 and 219; and Orenstein (2003), pp. 534–535</ref> A 1932 recording of the G major Piano Concerto was advertised as "Conducted by the composer",<ref>[[Columbia Graphophone Company|Columbia]] advertisement,''The Gramophone'', Volume 10, p. xv</ref> although he had in fact supervised the sessions while a more proficient conductor took the baton.<ref>Orenstein (2003), p. 536</ref> Recordings for which Ravel actually was the conductor included a ''Boléro'' in 1930, and a sound film of a 1933 performance of the D major concerto with Wittgenstein as soloist.<ref>Orenstein (2003), pp. 534–537</ref>