Abelian-symmetric 1-site C4v iPEPS

Specialized class for iPEPS with single abelian-symmetric on-site tensor possesing a (C4v) symmetry with respect to the permutation of its auxilliary indices

\[a_{suldr} = e^{i\theta} a_{s\textrm{p}(uldr)},\]

where \(\textrm{p}\) is a permutation associated to the symmetries of square lattice: rotations by \(\pi/2\) and reflections. This property in turn implies (\(A_1\)) symmetry for the double-layer tensor \(A_{(uu')(ll')(dd')(rr')}=a_{suldr}a_{su'l'd'r'}\).