  In the two-Higgs-doublet model, different Higgs doublets can be viewed as
components of a generic "hyperspinor". We decompose the Higgs potential of this
model into irreducible representations of the SU(2) group of transformations of
this hyperspinor. We discuss invariant combinations of the Higgs potential
parameters lambda_i that arise in this decomposition and provide simple and
concise sets of conditions for the hidden Z_2-symmetry, Peccei-Quinn symmetry,
and explicit CP-conservation in 2HDM. We show that some results obtained
previously by brute-force calculations are reduced to simple linear algebraic
statements in our approach.
