let the likelihood function be considered fixed; the likelihood function is usually well-determined from a statement of the data-generating process. it is clear that different choices of the prior distribution "p"("θ") may make the integral more or less difficult to calculate, and the product "p"("x"|"θ") × "p"("θ") may take one algebraic form or another. for certain choices of the prior, the posterior has the same algebraic form as the prior (generally with different parameter values). such a choice is a "conjugate prior".