the grothendieck–riemann–roch theorem from about 1956 is usually cited as the key moment for the introduction of this circle of ideas. the more classical types of riemann–roch theorem are recovered in the case where "s" is a single point (i.e. the final object in the working category "c"). using other "s" is a way to have versions of theorems 'with parameters', i.e. allowing for continuous variation, for which the 'frozen' version reduces the parameters to constants.