Quasihyperbolic geodesics in John domains. O. Martio; F.W. Gehring; K. Hag — 1989 Mathematica Scandinavica
Lipschitz Classes and the Hardy-Littlewood Property. K. Hag; K. Astala; P. Hag; V. Lappalainen — 1993 Monatshefte für Mathematik