Non-freeness of parabolic two-generator groups

Philip Choi, Kyeonghee Jo, Hyuk Kim +1

A complex number $\lambda$ is said to be non-free if the subgroup of $SL(2,\bc)$ generated by $$X=\begin{pmatrix} 1& 1\\ 0 & 1 \end{pmatrix} \,\, \text{and}\,\,\,Y_λ=\begin{pmatrix} 1& 0…