 Some homeomorphisms are not continuous deformations, such as the homeomorphism between a trefoil knot and a circle.An often-repeated mathematical joke is that topologists can't tell the difference between a coffee cup and a donut, since a sufficiently pliable donut could be reshaped to the form of a coffee cup by creating a dimple and progressively enlarging it, while preserving the donut hole in the cup's handle.A function formula_1 between two topological spaces is a homeomorphism if it has the following properties