module type S = sig type 'a t end
module type T = sig type 'a t = 'a list end
Line 1, characters 23-43:
1 | module type T = S with type -'a t = 'a list;;
                           ^^^^^^^^^^^^^^^^^^^^
Error: In this definition, expected parameter variances are not satisfied.
       The 1st type parameter was expected to be contravariant,
       but it is injective covariant.