ABSTRACT
The theory of conformal mapping shows that %' is an Rm arc which can terminate only at zo or at the boundary of D. We call %' theprincipal curve associated with the transition point z,, and denote D cut along V by Dl. In what follows we require ['I2 and ['I4 to have their principal values within Dl and be determined by continuity on the boundaries of Dl. On the other hand, any branch may be selected for f lJ4(z), provided that it is continuous in the closure of Dl; f -'J4(z) denotes the reciprocal of this branch.
