Euclidean geometry

According to the Twelfth Doctor, feigning surprise at the TARDIS' dimensional transcendentalism, three-dimensional Euclidean geometry had just been "torn up, thrown in the air, and snogged to death". (TV: The Husbands of River Song)

The "warped physics of hyperspace" were outside of Euclidean space. (PROSE: Uranus)

Euclidean geometry was distinguished from non-Euclidean geometry, (PROSE: Shadow of the Times Before, The Book of the Enemy) which characterised the intersections of space and time within the Time Vortex. (PROSE: Cat's Cradle: Witch Mark)

Once, while visiting ancient Athens with the Seventh Doctor, Melanie Bush corrected Euclid's geometry, much to his annoyance. (AUDIO: Mask of Tragedy)

Behind the scenes
Euclidean geometry is a specific mathematical conception of geometry consisting of five axioms. Most famously the ancients took the first four to be definitional and would attempt to justify the, leading to non-Euclidean geometry. However, has shown that this is not the only axiom that can be coherently denied given the proper approach.