{- Possible options for today: 1. (Un-)countability and introduction to alternate mathematical universes (so-called toposes), particularly one in which there are fewer real numbers than natural numbers [great basis for an Agda project, but right now not in Agda] 2. Program verification - Basic example - Insertion sort - Implementing a toy programming language ("the Hello World of Agda") 3. Issues with standard Agda, introduction to Cubical Agda 4. Exercises :-) 5. Stop -} {- Within the standard topos, it holds that: Within the standard topos, we can have a look at the following toposes: 1. Set 2. Eff We will notice: These two toposes are not the same. Withing the effective topos (Eff), we can have a look at the following toposes: 1. Set 2. Eff We will notice: These two toposes are* the same. (More precisely: This is only true if everywhere we replace Eff by Eff', where Eff' is a close cousin of Eff. The difference between Eff and Eff' is only visible in constructive mathematics, not in classical mathematics.) Withing the topos Sh(ℝ), we can have a look at the following toposes: 1. Set 2. Sh(ℝ) We will notice: These two toposes are not the same. -}