Unset Regular Subst Tactic.

Lemma same_abscissa_col : forall O E S U1 U2 A AX AY B BY C CY,
Cd O E S U1 U2 A AX AY -> Cd O E S U1 U2 B AX BY -> Cd O E S U1 U2 C AX CY ->
Col A B C.