Abraham Robinson's Non-standard analysis (http://en.wikipedia.org/wiki/Non-standard_analysis http://en.wikipedia.org/wiki/Non-standard_analysis) used a modern a

Abraham Robinson's Non-standard analysis (http://en.wikipedia.org/wiki/Non-standard_analysis http://en.wikipedia.org/wiki/Non-standard_analysis) used a modern axiomatic approach to legitimize Isaac Newton's intuitive use of infinitesimals, by creating a superset of the real numbers, some of which were smaller than any ordinary real (infinitesimals), or larger (infinite). He then went on to prove new things with it. And he started out as an engineer.