Metric spaces, completeness, contractions, compactness, the Arzela-Ascoli theorem, Picard's theorem, Weierstrass's theorem. Banach spaces, dual spaces, weak v's strong convergence. Hilbert spaces, ...
Notions of size for different kinds of mathematical objects are ubiquitous. The volume or of a set in Euclidean space (the study of which is fundamental to the field of Convex Geometry) and the ...