"The sources for the E flat major sonata are unanimous in naming J.S. Bach as the composer. In the case of the principal source this attribution is in the hand of C.P.E. Bach. This may ... be a case of collaboration between father and son. In all probability the G minor sonata was composed by C.P.E. Bach without his father's assistance"--4th prelim. p. Pref. in English and German.
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