On Finitely Generated Subgroups of a Free Product. Abraham Karrass; Donald Solitar Mathematische Zeitschrift
On the Failure of the Howson Property for a Group with a Single Defining Relation. Abraham Karrass; Donald Solitar Mathematische Zeitschrift
Subgroups of Infinite Index in Fuchsian Groups. A. Howard M. Hoare; Abraham Karrass — 1972 Mathematische Zeitschrift