[Haskell-cafe] Is a type synonym declaration really a synonym ?

Can someone confirm me that: type TA = A :+: B type TB = C :+: D type T = TA :+: TB is not equivalent to type T = A :+: B :+: C :+: D where I have defined infixr 6 :+: data (f :+: g) data A data B data C data D I have a computation at type level which is working with the later definition of T but not with the former (ghc 6.8.1) Thanks.