Section Compose.
Variables X Y Z X' Y' Z': Type.
Variable RY: relation2 Y Y'.
Variable RX: relation2 X X'.
Variable R1: relation2 X Y.
Variable R2: relation2 Y Z.
Variable RZ: relation2 Z Z'.
Variable S1: relation2 X' Y'.
Variable S2: relation2 Y' Z'.
Hypothesis H1: diagram RX R1 RY S1.
Hypothesis H2: diagram RY R2 RZ S2.

Theorem diagram_comp: diagram RX (comp R1 R2) RZ (comp S1 S2).