Christian Perfect and David Cushing spent the morning computing inverses using their special inverse blackboard.

Going left-to-right and top-to-bottom, we have:

- The inverse of a 2×2 matrix;
- The commutative diagram for the universal property of the inverse limit;
- A variable which is inversely proportional to another;
- The inverse of a complex number;
- The derivative of the inverse of a function;
- The inverse tangent of 1;
- The axiom for group inverses;
- Part of the definition of the logical inverse.

Thanks Christian and David for this wonderful idea!