The philosophy of mathematics.
Stanford Encyclopedia of Philosophy, Philosophy of Mathematics
Wikipedia, Philosophy of mathematics
David Corfield, Towards a Philosophy of Real Mathematics, Cambridge University Press (2003)
Roland Omnès, Converging Realities -- Toward a common philosophy of physics and mathematics, Princeton University Press, 2005
Paolo Mancosu, Philosophy of Mathematics and Mathematical Practice in the Seventeenth Century, OUP, 1996.
The role of Heraclitus: