Eric wrote:
>    a3 =3D a1.select { |e| a2.include?(e) }
>

compare:
   a3 =3D a1.select { |e| e.in? a2}

the latter is more straightforward. the former expression rocks my brain =
from left to right.

Can we see light for #in? in ruby2? (just asking since december is near =
:) and i do not see it in mauricio's eigenclass site either)

kind regards -botp