Accordingly, John Coltrane's "Giant Steps" (1960), with its 26 chords per 16 bars, can be played using only three pentatonic scales. Coltrane studied Nicolas Slonimsky's "Thesaurus of Scales and Melodic Patterns", which contains material that is virtually identical to portions of "Giant Steps". The harmonic complexity of "Giant Steps" is on the level of the most advanced 20th-century art music. Superimposing the pentatonic scale over "Giant Steps" is not merely a matter of harmonic simplification, but also a sort of "Africanizing" of the piece, which provides an alternate approach for soloing. Mark Levine observes that when mixed in with more conventional "playing the changes", pentatonic scales provide "structure and a feeling of increased space."