pseudocircle

Noun

 * 1)  The finite topological space X consisting of four distinct points { a, b, c, d } with the non-Hausdorff topology $$\left\{\{a,b,c,d\},\{a,b,c\},\{a,b,d\},\{a,b\},\{a\},\{b\},\emptyset\right\}$$.