Module type Gpr_interfaces.Specs.Deriv

module type Deriv = sig .. end
Derivatives of covariance functions

module Eval: Gpr_interfaces.Specs.Eval 
Derivatives always require evaluation functions
module Hyper: sig .. end
Hyper parameters that have derivatives
module Inducing: sig .. end
Derivatives of the covariance matrix of inducing inputs
module Inputs: sig .. end
Derivatives of the (cross-) covariance matrix of inputs.