Discrete and free groups acting on locally finite trees

We present an algorithm to decide whether or not a finitely generated subgroup of the isometry group locally finite simplicial tree is both discrete and free. The correctness this relies on following conjecture: every ‘minimal’ n-tuple isometries either contains elliptic element satisfies hypotheses Ping Pong Lemma. prove conjecture for n=2,3, show that it implies generalisation Ihara's Theorem.