With the aid of these canonical power series, [Schafer] derives numerous theorems concerning surfaces which osculate the given curve at the singular point, concerning the sections of the tangent developable in the neighbourhood of the singular point and concerning the projections of the given curve.

Make this lower case.
with the aid of these canonical power series, [schafer] derives numerous theorems concerning surfaces which osculate the given curve at the singular point, concerning the sections of the tangent developable in the neighbourhood of the singular point and concerning the projections of the given curve.