Editing Euler characteristic (section)

===Surfaces===
The Euler characteristic can be calculated easily for general surfaces by finding a polygonization of the surface (that is, a description as a [[CW-complex]]) and using the above definitions.
{| class="wikitable"
|-
!Name
!Image
!<abbr title="Euler characteristic">'''χ'''</abbr>
|-
|[[Interval (mathematics)|Interval]]
|[[Image:Complete graph K2.svg|100px]]
|'''{{0}}1'''
|-
|[[Circle]]
|[[Image:Cirklo.svg|100px]]
|'''{{0}}0'''
|-
|[[Unit disk|Disk]]
|[[Image:Disc Plain grey.svg|100px]]
|'''{{0}}1'''
|-
|[[Sphere]]
|[[Image:Sphere-wireframe.png|100px]]
|'''{{0}}2'''
|-
|[[Torus]] <br>''(Product of<br>two circles)''
|[[Image:Torus illustration.png|100px]]
|'''{{0}}0'''
|-
|[[Double torus]]
|[[Image:Double torus illustration.png|100px]]
|'''&minus;2'''
|-
|[[Triple torus]]
|[[Image:Triple torus illustration.png|100px]]
|'''&minus;4'''
|-
|[[Real projective plane|Real projective<br>plane]]
|[[Image:Steiners Roman.png|100px]]
|'''{{0}}1'''
|-
|[[Möbius strip]]
|[[Image:MobiusStrip-01.svg|100px]]
|'''{{0}}0'''
|-
|[[Klein bottle]]
|[[Image:KleinBottle-01.png|100px]]
|'''{{0}}0'''
|-
|Two spheres<br>(not connected) <br>''(Disjoint union<br>of two spheres)''
|[[File:2-spheres.png|200x200px]]
|2 + 2 = '''4'''
|-
|Three spheres<br>(not connected) <br>''(Disjoint union<br>of three spheres)''
|[[File:Sphere-wireframe.png|100x100px]][[File:Sphere-wireframe.png|100x100px]][[File:Sphere-wireframe.png|100x100px]]
|2 + 2 + 2 = '''6'''
|-
|<math>n</math> spheres<br>(not connected) <br>''(Disjoint union<br>of ''n'' spheres)''
| [[File:Sphere-wireframe.png|100x100px]]'''<big> ...</big>'''[[File:Sphere-wireframe.png|100x100px]]
|{{nowrap|2 + ... + 2 {{=}} '''2n'''}}
|}