## Fall 2015 Seminar Errata

#### John Baez

• Lecture 1, Jordan Tousignant's notes - "The real plane is the affine scheme $$\mathbb{Z}[x,y]$$" is not correct. The affine scheme corresponding to the commutative ring $$\mathbb{Z}[x,y]$$ is called simply 'the plane'. Its 'real points' are defined to be the homomorphisms from this ring to $$\mathbb{R}$$; there is one for each point in $$\mathbb{R}^2$$, since the generators $$x$$ and $$y$$ can be sent to arbitrary real numbers.
• Lecture 7, Jordan Tousignant's notes - The moduli space of triangles is not $$[0,\infty)^3$$, but only the subset consisting of triples obeying the triangle inequality.

The Riemann sphere is $$\mathbb{C} \cup \{\infty\}$$, not $$\mathbb{C} \cup \{0\}$$.

baez@math.removethis.ucr.andthis.edu