cannot field pedagogical h jerome keisler david tall educators maintain use infinitesimals intuitive easily grasped students epsilon delta approach analytic concepts ref name ec h jerome keisler ''elementary calculus infinitesimal approach'' first edition nd edition http wwwmathwiscedu keisler calchtml full text nd edition ref approach sometimes provide easier proofs results corresponding epsilon delta formulation proof much simplification comes applying easy rules nonstandard arithmetic follows infinitesimal finite infinitesimal infinitesimal infinitesimal infinitesimal together
Formal science Mathematics Pure mathematics Analysis Non-standard analysis