module Gpr_cov_const:sig
..end
k(x, y) = 1/s^2
logtheta = log(s)
module Params:sig
..end
module Eval:Eval
with type Kernel.params = Params.t
with type Inducing.t = int
with type Input.t = unit
with type Inputs.t = int
module Deriv:Deriv
with module Eval = Eval
with type Hyper.t = [ `Log_theta ]