68 4. INJECTIVITY CRITERIA
in D. Hence h is constant in D, g = af + b where a and b are constants, and g is
injective in D. Thus
c
T(D) 2:: 4 > 0
and Dis a quasidisk by Theorem 4.1.14. D
It would be interesting to know if there exists an analogue of Theorem 4.4.1
for the Jacobian of a quasiconformal mapping.