error in the example in assignment2, lines 73 -77 (cancelation in groups).

[yitzhak-zangi]

the equation a⁻¹ * b * c * c⁻¹ * a * b⁻¹ * a * a⁻¹ = 1 isn't true in general (it simplifies to a⁻¹ * b * a * b⁻¹).