type SumOp () =
    static member operator x =
        fun y -> x + y

type Number<'a> = { i : int }

let inline foobar (b : Number<'a>)  =
        (^a : (static member operator : int -> ^rest) b.i)

let b : Number<SumOp> = {i = 5}
SumOp.operator 2 3
let func : int -> int = foobar b