This study is part of a larger research program aimed at studying mental mathematics with objects other than numbers. It concerns operations on functions in a graphical environment with Grade-11 students. Grounded in the enactivist theory of cognition, particularly in problem-posing, the study aims to characterize students' mathematical activity in this mental mathematics environment. The data analysis offers understandings of strategies that students brought forth: algebraic/parametric, graphical/geometric, numerical/graphical. These are discussed in relation to implications for research on solving processes and potential for studying functions. [For the complete proceedings, see ED597799.]