# Why is “Amenable Group” a pun?

"The original definition, in terms of a finitely additive invariant measure (or mean) on subsets of G, was introduced by John von Neumann in 1929 under the German name "messbar" ("measurable" in English) in response to the Banach–Tarski paradox. In 1949 Mahlon M. Day introduced the English translation "amenable", apparently as a pun." http://en.wikipedia.org/wiki/Amenable_group

I'm not a native speaker and I don't get the pun :)

• Amenable, pleasant. The word is pronounced like "a-mean-able, so sort of mean-able, able to support a mean. – André Nicolas Aug 24 '13 at 21:58
• thanks! didnt know it's pronounced like this – Bananach Aug 24 '13 at 22:04
• I don't pronounce it like that :) – Ted Shifrin Aug 24 '13 at 22:24
• This is also discussed on the talk page of the Wikipedia article on Amenable groups. – Martin Sleziak Mar 15 '17 at 14:45

Amenable (discrete) groups were first considered by J. von Neumann, albeit under a di fferent name ([Neu]). The first to use the adjective "amenable" was M. M. Day in [Day], apparently with a pun in mind: These groups $G$ are called amenable because they have an invariant mean on $L^\infty(G)$, but also since they are particularly pleasant to deal with and thus are truly amenable - just in the sense of that adjective in colloquial English.