Skip to main content
2 of 5
added 118 characters in body
Tony Huynh
  • 32.1k
  • 11
  • 112
  • 187

Yes, this is true. We proceed by induction on $|V(G)|+|E(G)|$. Since $G$ is $2$-connected, $G$ has an ear decomposition $(C, P_1, \dots, P_k)$, with $u \in V(C)$. If $G$ is just a cycle, then the claim is true (see the comment of okw1124 above), so we may assume that $k \geq 1$. If the last ear $P_k$ is just an edge $e$, then $G \setminus e$ is $2$-connected, and we can apply induction. Thus, we may assume $|V(P_k)| \geq 3$. Suppose $P_k=x_1x_2 \dots x_\ell$. Since $G'=G-\{x_2, \dots, x_{\ell-1}\}$ is $2$-connected, $G'$ contains two spanning trees $T_1'$ and $T_2'$ such that for all $v \in V(G') \setminus \{u\}$, the $uv$-paths in $T_1'$ and $T_2'$ are internally-disjoint. Let $T_1=T_1' \cup x_1x_2 \dots x_{\ell-1}$ and $T_2:=T_2' \cup x_2x_3 \dots x_\ell$. It suffices to show that for all $v \in \{x_2, \dots, x_{\ell-1}\}$, the $uv$-paths in $T_1$ and $T_2$ are internally-disjoint. This follows from the fact that the $ux_1$-paths in $T_1$ and $T_2$ are internally-disjoint, the $ux_\ell$-paths in $T_1$ and $T_2$ are internally-disjoint, and the two paths $x_1 x_2 \dots v$ and $x_\ell x_{\ell-1} \dots v$ are internally-disjoint.

Tony Huynh
  • 32.1k
  • 11
  • 112
  • 187