Chang's Conjecture with $\square_{ω_1, 2}$ from an $ω_1$-Erdős Cardinal
Answering a question of Sakai, we show that the existence of an $ω_1$-Erdős cardinal suffices to obtain the consistency of Chang's Conjecture with $\square_{ω_1, 2}$. By a result of Donder this is best possible. We also give an answer to another question of Sakai relating to the incompatibility of $\square_{λ, 2}$ and $(λ^+, λ) \twoheadrightarrow (κ^+, κ)$ for uncountable $κ$.