Computer Algebra Systems (CAS) provide sophisticated functionality to assist with mathematical problem solving. Despite their widespread adoption, however, little work in the HCI community has examined the extent to which these computational tools support domain experts. In this paper, we report findings from a qualitative study investigating the work practices and tools of nine mathematicians in a research setting. Counter to our expectations, our data suggests that computational tools play only a minor role in their workflow, with the limited use of CAS owing primarily to four factors: (1) the need for transparency in CAS's reasoning to explain computed results; (2) the problem of rigidity and formality in CAS's input/output style dialogue; (3) the need for 2D input to support a wide range of annotations, diagrams, and in-place manipulation of objects of interest; and (4) the need for collaboration, particularly in early stages of problem solving. While grounded in the stu...