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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def k_xx(self,t,tprime,s,sprime,l):
 """Covariance between observed values. s and t are one domain of the integral (i.e. the integral between s and t) sprime and tprime are another domain of the integral (i.e. the integral between sprime and tprime) We're interested in how correlated these two integrals are. Note: We've not multiplied by the variance, this is done in K."""

        return 0.5 * (l**2) * ( self.g((t-sprime)/l) + self.g((tprime-s)/l) - self.g((t - tprime)/l) - self.g((s-sprime)/l))