However, as the following theorem shows, this is possible only if the weight
function is not injective.
-\thmn{MST uniqueness}%
+\thmn{Uniqueness of MST}%
If all edge weights are distinct, then the minimum spanning tree is unique.
\proof
$T_1$ and $T_2$ must be identical.
\qed
+\nota\id{mstnota}%
+When $G$ is a graph with distinct edge weights, we will use $\mst(G)$ to denote
+its unique minimum spanning tree.
+
\rem\id{edgeoracle}%
To simplify the description of MST algorithms, we will expect that the weights
of all edges are distinct and that instead of numeric weights (usually accompanied
original graph. In the few cases where we need a more concrete input, we will
explicitly state so.
-\nota\id{mstnota}%
-When $G$ is a graph with distinct edge weights, we will use $\mst(G)$ to denote
-its unique minimum spanning tree.
-
Another useful consequence is that whenever two graphs are isomorphic and the
-isomorphism preserves weight order, the isomorphism applies to their MST's
-as well:
+isomorphism preserves the relative order of weights, the isomorphism applies to their MST's as well:
\defn
A~\df{monotone isomorphism} of two weighted graphs $G_1=(V_1,E_1,w_1)$ and
for each $e,f\in E_1: w_1(e)<w_1(f) \Leftrightarrow w_2(\pi[e]) < w_2(\pi[f])$.
\lemman{MST of isomorphic graphs}\id{mstiso}%
-Let~$G_1$ and $G_2$ be two weighted graphs with unique edge weights and $\pi$
+Let~$G_1$ and $G_2$ be two weighted graphs with distinct edge weights and $\pi$
their monotone isomorphism. Then $\mst(G_2) = \pi[\mst(G_1)]$.
\proof