# Definition:Combinable/Relations

$(1): \quad \mathcal R_1 \subseteq S_1 \times T_1$ be a relation on $S_1 \times T_1$
$(2): \quad \mathcal R_2 \subseteq S_2 \times T_2$ be a relation on $S_2 \times T_2$
If $\mathcal R_1$ and $\mathcal R_2$ agree on $S_1 \cap S_2$, they are said to be combinable.