<s>
A	O
conc-tree	O
is	O
a	O
data	B-General_Concept
structure	I-General_Concept
that	O
stores	O
element	O
sequences	O
,	O
and	O
provides	O
amortized	O
O(1 )	O
time	O
append	O
and	O
prepend	O
operations	O
,	O
O(log n )	O
time	O
insert	O
and	O
remove	O
operations	O
and	O
O(log n )	O
time	O
concatenation	O
.	O
</s>
<s>
This	O
data	B-General_Concept
structure	I-General_Concept
is	O
particularly	O
viable	O
for	O
functional	O
task-parallel	O
and	O
data-parallel	O
programming	O
,	O
and	O
is	O
relatively	O
simple	O
to	O
implement	O
compared	O
to	O
other	O
data-structures	O
with	O
similar	O
asymptotic	O
complexity	O
.	O
</s>
<s>
Orthogonally	O
,	O
they	O
are	O
used	O
to	O
efficiently	O
aggregate	O
data	O
in	O
functional-style	O
task-parallel	B-Operating_System
algorithms	I-Operating_System
,	O
as	O
an	O
implementation	O
of	O
the	O
conc-list	O
data	O
abstraction	O
.	O
</s>
<s>
Conc-list	O
is	O
a	O
parallel	O
programming	O
counterpart	O
to	O
functional	B-Protocol
cons-lists	I-Protocol
,	O
and	O
was	O
originally	O
introduced	O
by	O
the	O
Fortress	B-Language
language	I-Language
.	O
</s>
<s>
The	O
<>	O
type	O
represents	O
inner	O
nodes	O
,	O
and	O
is	O
pronounced	O
conc	O
,	O
inspired	O
by	O
::	O
(	O
the	O
cons	B-Protocol
type	O
)	O
in	O
functional	O
lists	O
,	O
used	O
for	O
sequential	O
programming	O
.	O
</s>
<s>
It	O
was	O
shown	O
that	O
these	O
basic	O
operations	O
can	O
be	O
extended	O
to	O
support	O
worst-case	O
O(1 )	O
deque	B-Application
operations	O
,	O
while	O
keeping	O
the	O
O(log n )	O
concatenation	O
time	O
bound	O
,	O
at	O
the	O
cost	O
of	O
increasing	O
the	O
constant	O
factors	O
of	O
all	O
operations	O
.	O
</s>
