Various higher-order fuzzy set theories (HO-FSTs) have been developed since 1960s.
2">Painstaking efforts have been devoted to devising basic measures for these HO-FSTs.
We present a unified representation for several of these HO-FSTs, based on u-map.
This effectively dissolves the artificial boundaries between different HO-FSTs.
Theoretical developments in HO-FSTs can now be done in a much more unified manner.