the.com/topology
the math where a coffee mug and a donut are secretly the same shape
means The branch of mathematics studying the properties of shapes that survive stretching, bending, and twisting—but not tearing or gluing—so it cares about holes and connectedness rather than exact measurements.
from From the Greek 'topos' (place) plus '-logia' (study of), so literally 'the study of place.' The term entered mathematics in the 19th century; an earlier name was the Latin 'analysis situs,' meaning 'analysis of position.' The same 'topos' gives us 'topic' and 'utopia' (literally 'no-place').
hole countingCares about holes, not distances or angles
famous proofPerelman solved Poincaré, refused a million dollars
hairy ballYou cannot comb a hairy sphere flat
rubber sheetStretch and bend freely, just never tear
map coloringFour colors suffice for any flat map