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Easy unitary quantum groups are a particular class of compact matrix quantum groups introduced by Freslon and Weber in [FreWeb16], generalizing the definition of easy orthogonal quantum groups given by Banica and Speicher in [BanSp09]. Every easy unitary quantum group is by definition a compact quantum subgroup of a free unitary quantum group.
Informally, a compact matrix quantum group is called easy unitary if it is a compact quantum subgroup of the corresponding free unitary quantum group and if its corepresentation category is generated by a category of partitions. Formally, for every , any compact
-matrix quantum group
is called an easy unitary quantum group if the corepresentation category
of
has as objects the set
of tuples of arbitrary lengths with two distinct possible entries
and
and if there exists some category of two-colored partitions
such that for all
and all
the morphism set
of
is given by
where for all the linear map
satisfies for all
,
where is the standard basis of
and where for all
the symbol
is
if the kernel, i.e., the induced partition with
upper and
lower points, of
refines
and is
otherwise.