Your playground

Choose a point. Discover its neighbourhood.

Click to show · Click again to remove

Point & neighbourhood

Optional. The full open sets are already shown.

Point to a vertex or focus it with Tab. Its details appear here, beside the graph.

Vertex neighbourhoods
See the exact sets

N(v) is the smallest open set containing v. The largest open set containing any vertex is always the whole graph.

Edit this graph & drawing
A ⊆ V:

Active quotient

Order and classes

Inspector

Selected set A