\begin{definition}[Definition:Combinable/Mappings]
Let:
:$(1): \quad f_1: S_1 \to T_1$ be a mapping from $S_1$ to $T_1$
:$(2): \quad f_2: S_2 \to T_2$ be a mapping from $S_2$ to $T_2$
If $f_1$ and $f_2$ agree on $S_1 \cap S_2$, they are said to be '''combinable'''.
\end{definition}