[x] unit test that 4*i lies on the 1/2 pleating ray and 37 lies on the 0/1 pleating ray and -43 lies on the 1/1 pleating ray (parabolic/parabolic case)
[X] unit test that riley_string X riley_string^-1 Y = farey_string
[x] unit test fixed points and words are equal to finite initial list
[x] verify trace of farey words equals value of farey polynomials