The Pfaff method, on the other hand, cannot handle (3.1) by itself.
It must simultaneously prove that [3, p. 2, eq.(2.3),]
Pfaff's method proceeds now as in Section 2. Here we find directly
Pfaff's method then concludes by the observation that the
right-hand sides of (3.1) and (3.6) also satisfy (3.7) and (3.8).
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