Asymptotic Values of Functions Holomorphic in the Unit Disk. Frank B. Ryan; Karl F. Barth — 1967 Mathematische Zeitschrift
Infinitely many asymptotic values of locally univalent meromorphic functions. Barth, Karl F.; Rippon, Philip J. — 2003 Annales Academiae Scientiarum Fennicae. Mathematica
Asymptotic tracts of harmonic functions. III. Barth, Karl F.; Brannan, David A. — 1996 International Journal of Mathematics and Mathematical Sciences