In this chapter we investigate the role of Computer Algebra Systems (CAS) in textbook proofs. We describe two cases of CAS use in textbook proofs and use the instrumental approach, and in particular the distinction between epistemic and pragmatic mediations, to understand the consequences of the so-called CAS-assisted proofs. We end with a discussion of the experienced shortcomings of the instrumental approach in relation to CAS use in justification of mathematical results, and suggest the inclusion of alternative frameworks for filling the gap.