Dear All, We are delighted to present the MaPSS Seminar topic of today; please see the abstract below. **From this Semester the Seminar will always run on Monday, at 5:00pm in 535A** Following the talk, there will be pizza on offer. Speaker: Gennady Notowidigdo (UNSW) Title: Rational trigonometry of a tetrahedron Abstract: This talk outlines a trigonometry for a general tetrahedron in three-dimensional space, using the framework of rational trigonometry (as developed by NJ Wildberger). Concepts from one-dimensional and two-dimensional affine trigonometry are built on to obtain some results pertaining to the trigonometric quantities of the tetrahedron. Some examples are given. Supervisors, please encourage your students to attend. Thanks, MaPSS Organizers