infix  1  <!  <@
infix  2 <!! <@@
infixr 1  !>  @>
infixr 2 !!> @@>

infix 0 &
infix 9 &&

datatype ('a, 'b) t1 = & of 'a * 'b
datatype ('a, 'b) t2 = && of 'a * 'b

(* error *)
local
   fun fst x && y = x
in
end

(* defines fst *)
local
   fun fst (x && y) = x
in
   val _ = fst
end

(* error *)
local
   fun fst x <! y = x
in
end

(* error *)
local
   fun fst (x <! y) = x
in
end

(* error *)
local
   fun f = ()
in
end

(* defines f *)
local
   fun f _ = ()
in
   val _ = f
end

(* defines f *)
local
   fun f _ _ = ()
in
   val _ = f
end

(* defines f *)
local
   fun f _ _ _ = ()
in
   val _ = f
end

(* defines f *)
local
   fun f _ _ _ _ = ()
in
   val _ = f
end

(* defines f *)
local
   fun f _ _ _ _ _ = ()
in
   val _ = f
end

(* error *)
local
   fun _ = ()
in
end

(* error *)
local
   fun _ _ = ()
in
end

(* error *)
local
   fun _ _ _ = ()
in
end

(* error *)
local
   fun _ _ _ _ = ()
in
end