  The hexagonal superconductor SrPtAs exhibits time-reversal-symmetry breaking
below $T_c$, hinting at an unconventional pairing state. Therefore, the
symmetry of the underlying crystal is important for the classification of
possible gap structures and their mixing. Here, we use the generating point
group D$_{6h}$ of SrPtAs for a comprehensive classification of the gap
functions and to construct a tight-binding model. Our work clarifies questions
of symmetry and topology in this non-symmorphic material and allows for better
comparison with other hexagonal systems.
