dually represents both process (as h gets small) and concept (the limit itself). This causes further difficulties because it is not computed by a finite set of calculations (Cornu, 1991). Instead, in a specific case such as f(x)=x2, first the simplification is
performed assuming h¹0, then the final result is computed by setting h=0. For other expressions this confusing limit process soon becomes too complicated and derivatives are computed by a collection of rules.