Set: pp::colors
  Set: pp::unicode
  Proved: trans_refl_right
  Proved: trans_refl_left
  Proved: trans_assoc
  Proved: symm_trans
  Assumed: a1
  Assumed: a2
  Assumed: a3
  Assumed: a4
  Assumed: Ax1
  Assumed: Ax2
  Assumed: Ax3
  Assumed: Ax4
symm (trans (trans (trans (refl a1) (trans (trans Ax1 (refl a2)) Ax2)) (refl a3)) (trans Ax3 Ax4))
trans (symm Ax4) (symm Ax1)