“…Over the course of the years, results concerning free products and amalgamated products [9,11,12,14], and HNN extensions [10], of linear groups have appeared. Shalen [12] in particular proved that amalgamated products of linear groups over C, amalgamated over maximal cyclic subgroups, are linear over Cptq, where t is an indeterminate, and therefore also linear over C (compare [12,Lemma 1.2], or Lemma 2.8), and that the class of linear groups over C is preserved under taking free products (compare [12,Theorem 1]).…”