Figure 6: Two equivalent descriptions of the boundary of 2D SPT model with
symmetry.
From: Symmetry-protected topological phases from decorated domain walls

(a) thick bonds represent Z2 variable in state
and thin bonds
, spin 1/2 exists on their domain wall. (b) One Z2 variable per bond and one spin variable per vertex. Time reversal acts on spins in a way dependent of neighboring Z2 configurations. Dotted boxes represent local degrees of freedom on the 1D boundary labelled by group elements.
symmetry.