This may be inappropriate for MO, but here goes: if I have understood the statement of the Erdős–Rado theorem correctly, then it contains as a special case the following result:
if $\mu$ is an infinite cardinal then $(2^\mu)^+ \to (\mu^+)_\mu^2$
that is, every $\mu$-colouring of the $2$-elements subsets of a set $X$ of cardinality $> 2^\mu$ has a monochromatic subset of cardinality $>\mu$.
Looking online, the usual citation given for the ER-theorem is
P. Erdős, R. Rado, A partition calculus in set theory. Bull. Amer. Math. Soc. 62 (1956), 427–489
I am trying to track down where in this paper one can find the statement of the E-R theorem, or at least the special case described above. Unfortunately, partition calculus lies well outside my usual routes for mathematical excursions, and some of the notation E&R use seems slightly at odds with the notation I see in all the various online notes describing or proving the E-R theorem. I am hoping that the set theorists among the MO readership may be more familiar with the notation of the paper and hence be able to quickly locate the statement.