Equations were a part of mathematics.
Dr Who, the "greatest human mathematician", figured out the equations that unified the concepts of Space and Time into the Idea of the Living Matter, allowing him to conceive and construct his dimensionally-transcendental timeship the TARDIS. (PROSE: The Equations of Dr Who)
After spending Christmas with his grandmother and aunt in 2004, Matiu worked on time travel equations and sent himself to Christmas Eve, 1953, the time when his grandfather disappeared. (PROSE: Water's Edge)