German Mathematician and Philosopher of Mathematics...
Frege's work with Mathematics was foundational to modern logic and
he introduced such working concepts as the conditional and the
variable. He also worked on the status of arithmetic's and, although
some his proofs were later proved incomplete by Russell, was largely responsible
for the establishment of the basic concepts of math on a logical basis.


Beyond Maths.
He also wrote extensively on language in relation to logic, examining
ideas like sense, reference, (which Deleuze draws extensively on) concept,
identity, assertion/negation. His writings established such ideas as a legitimate
area for philosophical investigation, and must be seen as the beginning of
the twentieth centuries contest with language and meaning.

