let Foo (a : (int * int) seq) =  ();;
val Foo : seq<int * int> -> unit

let inline Bar (a : (a' * int) seq) = ();;
let Bar (a : (a' * int) seq) =
--------------^^
stdin(8,15): error FS0039: The type 'a'' is not defined
>

let Bar<'a> (a: ('a * int) seq) = ()