I'm trying to understand a text, 'Dynamics on Time Scales'. Some of you may be familiar with this subject. Unfortunately, the first page has already confused me. So it appears that I'm either a math retard or it's been so long since my university courses that new things have arisen that I'm not aware of. I'm going to be optimistic and choose the latter option. So, have the following new functions (like cos, sin, etc.) been defined during my absence from the field: 'inf' and 'sup' ? , and if so, what the hell do they mean ? or am I so mathematically inept that I cannot grasp the basic definitions required to discuss the topic?