Movement based on 2 contrasting themes, both subjected to variation procedure. Varied melodies, harmonies (major/minor), rhythms, tempo, and accompaniment.
http://www.wwnorton.com/college/music/listeninglab/shared/li...

with second subject transposed in the reprise) is subjected to cumulative variation treatment,
https://books.google.com/books?id=spdmAgb78xwC&pg=PA115&lpg=...

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Note added at 28 mins (2019-04-18 14:35:47 GMT)
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MUS 312 Form & Analysis
F. Variation Procedures
A variation is simply a restatement of any musical entity that retains some elements of the original and changes others.

Procedures organized by the uninterrupted repetition of a short melodic or harmonic unit are termed: continuous variations.

Procedures whose themes and variations are closed, complete structural units are termed: sectional variations.
http://spider.georgetowncollege.edu/music/burnette/Mus312/31...
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for Piano, and Old Norwegian Melody with Variations, Op.51, for Two Pianos: An Analytical Overview and Interpretive Study of the Variation Procedure
https://etd.ohiolink.edu/!etd.send_file?accession=osu1257892...