...

s that allows us to use just two triangles in the standard square planar representation of a torus with opposite edges identified. While this means that all three corners of each triangle is actually identified with one point, if we go through the algebraic formalities of computing the homology groups, we get the same answer as with a more complicated geometrical simplical subdivision. So we actually make the computation, discuss some generalities on subgroups of Z plus Z, and then move to the computation of the homology of the projective plane, for which a new phenomenon appears called torsion: a homology group which is actually a finite commutative group, not a free abelian group. In fact H_1 (P) is just Z/2Z or Z_2, the group with two elements. This corresponds to a cycle which is not a boundary, but which has the property that twice that cycle is a boundary! Then we introduce the Betti numbers b_0, b_1, b_2 etc. which are the ranks of the homology groups H_0, H_1, H_2 etc, and mention the celebrated result that the alternating sum of Betti numbers gives us the Euler characteristic of the space. This is the last lecture in this series for a while! ************************ Screenshot PDFs for my videos are available at the website http://wildegg.com. These give you a concise overview of the contents of the lectures for various Playlists: great for review, study and summary. My research papers can be found at my Research Gate page, at https://www.researchgate.net/profile/Norman_Wildberger My blog is at http://njwildberger.com/, where I will discuss lots of foundational issues, along with other things. Online courses will be developed at openlearning.com. The first one, already underway is Algebraic Calculus One at https://www.openlearning.com/courses/algebraic-calculus-one/ Please join us for an exciting new approach to one of mathematics' most important subjects! If you would like to support these new initiatives for mathematics education and research, please consider becoming a Patron of this Channel at https://www.patreon.com/njwildberger Your support would be much appreciated. *********************** Here are all the Insights into Mathematics Playlists: Elementary Mathematics (K-6) Explained: https://www.youtube.com/playlist? list=PL8403C2F0C89B1333 Year 9 Maths: https://www.youtube.com/playlist?list=PLIljB45xT85CcGpZpO542YLPeDIf1jqXK Ancient Mathematics: https://www.youtube.com/playlist?list=PLIljB45xT85Aqe2b4FBWUGJdYROT6-o4e Wild West Banking: https://www.youtube.com/playlist?list=PLIljB45xT85DB7CzoFWvA920NES3g8tJH Sociology and Pure Mathematics: https://www.youtube.com/playlist?list=PLIljB45xT85A-qCypcmZqRvaS1pGXpTua Old Babylonian Mathematics (with Daniel Mansfield): https://www.youtube.com/playlist? list=PLIljB45xT85CdeBmQZ2QiCEnPQn5KQ6ov Math History: https://www.youtube.com/playlist?list=PL55C7C83781CF4316 Wild Trig: Intro to Rational Trigonometry: https://www.youtube.com/playlist?list=PL3C58498718451C47 MathFoundations: https://www.youtube.com/playlist?list=PL5A714C94D40392AB Wild Linear Algebra: https://www.youtube.com/playlist?list=PLIljB45xT85BhzJ-oWNug1YtUjfWp1qAp Famous Math Problems: https://www.youtube.com/playlist?list=PLIljB45xT85Bfc-S4WHvTIM7E-ir3nAOf Probability and Statistics: An Introduction: https://www.youtube.com/playlist?list=PLIljB45xT85AMigTyprOuf__daeklnLse Boole's Logic and Circuit Analysis: https://www.youtube.com/playlist?list=PLIljB45xT85CnIGIWb7tH1F_S2PyOC8rb Universal Hyperbolic Geometry: https://www.youtube.com/playlist?list=PLIljB45xT85CN9oJ4gYkuSQQhAtpIucuI Differential Geometry: https://www.youtube.com/playlist?list=PLIljB45xT85DWUiFYYGqJVtfnkUFWkKtP Algebraic Topology: https://www.youtube.com/playlist?list=PL6763F57A61FE6FE8 Math Seminars: https://www.youtube.com/playlist?list=PLBF39AFBBC3FB30AF ************************ And here are the Wild Egg Maths Playlists: Triangle Centres: https://www.youtube.com/watch?v=iLBGXDSUohM&list=PLzdiPTrEWyz6VcJQ5xcuqY6g4DWjvpmjM Six: An elementary course in pure mathematics: https://www.youtube.com/playlist?list=PLzdiPTrEWyz4KD007Ge10dfrDVc4YwlYS Algebraic Calculus One: https://www.youtube.com/playlist?list=PLzdiPTrEWyz4rKFN541wFKvKPSg5Ea6XB Algebraic Calculus Two: https://www.youtube.com/playlist?list=PLzdiPTrEWyz5VLVr-0LPPgm4T1mtU_DG- м