The document discusses four key themes of activity theory:
1. Instrumental and semiotic layers of mediation in activity including talk, text, pictures, gestures, sounds, tools, and signs.
2. Contradictions and history making through re-mediation, double stimulation, and agency.
3. A transcript is provided as an example of instrumentalities in activity between two workers.
4. The harmonica model is referenced as representing the different layers of activity.