Type.Polymorphic4_inputSee module Polymorphic_input: very same functions with three additional arguments corresponding to the additional type variables.
val structural_descr :
Structural_descr.t ->
Structural_descr.t ->
Structural_descr.t ->
Structural_descr.t ->
Structural_descr.tval reprs : 'a -> 'b -> 'c -> 'd -> ('a, 'b, 'c, 'd) t list