Published online by Cambridge University Press: 12 March 2014
We show, for any ordinal γ ≥ 3, that the class ℜaCAγ is pseudo-elementary and has a recursively enumerable elementary theory. ScK denotes the class of strong subalgebras of members of the class K. We devise games, Fn (3 ≤ n ≤ ω), G, H, and show, for an atomic relation algebra  with countably many atoms, that
 with countably many atoms, that

for 3 ≤ n < ω. We use these games to show, for γ > 5 and any class K of relation algebras satisfying

that K is not closed under subalgebras and is not elementary. For infinite γ, the inclusion ℜaCAγ ⊂ ScℜaCAγ is strict.
For infinite γ and for a countable relation algebra  we show that
 we show that  has a complete representation if and only if
 has a complete representation if and only if  is atomic and ∃ has a winning strategy in F (At(
 is atomic and ∃ has a winning strategy in F (At( )) if and only if
)) if and only if  is atomic and
 is atomic and  ∈ ScℜaCAγ.
 ∈ ScℜaCAγ.