# Properties of Line Integrals question

• I
• WMDhamnekar
In summary, the author is working on trying to find an answer to the question of whether or not an equilateral triangle contradicts Pythagoras theorem.f
I mean, don’t lose track of the underlying purpose of that example: To demonstrate an application of Green’s theorem to a region with holes in it where the boundary is not a single closed curve but a union of several closed curves. In those cases Green’s theorem relates the sum of the line integrals over those closed curves to a surface integral over the contained region.

I do disagree somewhat with figure 4.3.4. There is no need to cut the region into several regions. It is enough to introduce enough cuts to make a single bounded region without holes. I used this myself last year when installing guiding cable for a lawnmower robot in my garden.

I mean, don’t lose track of the underlying purpose of that example: To demonstrate an application of Green’s theorem to a region with holes in it where the boundary is not a single closed curve but a union of several closed curves. In those cases Green’s theorem relates the sum of the line integrals over those closed curves to a surface integral over the contained region.

I do disagree somewhat with figure 4.3.4. There is no need to cut the region into several regions. It is enough to introduce enough cuts to make a single bounded region without holes. I used this myself last year when installing guiding cable for a lawnmower robot in my garden.
Just one question:
Does author want to say Green's theorem holds for 'multiple connected regions' instead of ' multiply connected regions' ?
If no, would you distinguish between 'multiple connected regions' and 'multiply connected regions'

Just one question:
Does author want to say Green's theorem holds for 'multiple connected regions' instead of ' multiply connected regions' ?
If no, would you distinguish between 'multiple connected regions' and 'multiply connected regions'
No. Yes.

The concept of being multiply connected is a topological concept that effectively tells you that a region has holes in it. It is in contrast to simply connected region.

WMDhamnekar
Imagine a connected region in the plane bounded by a finite number of closed curves. a transverse cut is a path in the region whose endpoints lie on the boundary. such a region is simply connected, or 1-conncted, if any transverse cut separates it into two pieces, and a region is n+1 connected if any transverse cut that does not separate it, changes it into an n connected region. E.g. a region is doubly connected if any transverse cut separates it into a simply connected region. I.e. an annulus, the region between two concentric circles, is doubly connected. Removing n disjoint discs from the interior of a disc gives an n+1 connected region.

these definitions are taken from Riemann's paper on the theory of abelian functions, where he introduced these ideas, (and apparently created the subject of topology).

see the simply connected (einfach zusammenhangende) and doubly connected (zweifach zusammenhangende) surfaces depicted on page 9 of his paper: (which are similar to figures in your posts 29, 34)

https://www.maths.tcd.ie/pub/HistMath/People/Riemann/AbelFn/AbelFn.pdf

Last edited:
Orodruin