(** Reversing diagrams *)
Section Reverse.
Variables X X' Y Y': Type.
Variable RX: relation2 X X'.
Variable R:  relation2 X Y.
Variable RY: relation2 Y Y'.
Variable R': relation2 X' Y'.
Hypothesis H: diagram RX R RY R'.

Theorem diagram_reverse: diagram R RX R' RY.
End Reverse.