In this paper, we show that if
K ⊂ ℂ is AD-regular and sufficiently flat, then K is a subset of a chord-arc curve if
the Cauchy integral operator is bounded on L2(K). This result partially answers a
question raised by G. David, P. Jones and S. Semmes. Also, we prove that if K is as
above (locally) and has positive analytic capacity, then K must contain a subset
of a rectifiable curve of positive length. Finally, we characterize subsets of
some quasicircles in terms of a simple geometric condition invented by P.
Jones.