hello caml-list
thanks for all the help so far; it's been very educational
there's a type error I can't get my head around:

class a =
object
end

and b =
object
inherit a
method d (e : b) = (e :> a)
end

gives the error:

The abbreviation b expands to type < d : b -> a > but is used with type < >

why is this?