a__first
0
X
nil
a__first
s
X
cons
Y
Z
cons
mark
Y
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X
Z
a__from
X
cons
mark
X
from
s
X
mark
first
X1
X2
a__first
mark
X1
mark
X2
mark
from
X
a__from
mark
X
mark
0
0
mark
nil
nil
mark
s
X
s
mark
X
mark
cons
X1
X2
cons
mark
X1
X2
a__first
X1
X2
first
X1
X2
a__from
X
from
X
2.2
mark
cons
X1
X2
mark
X1
mark
s
X
mark
X
mark
first
X1
X2
mark
X2
mark
first
X1
X2
a__first
mark
X1
mark
X2
a__from
X
mark
X
mark
from
X
a__from
mark
X
a__first
s
X
cons
Y
Z
mark
Y
mark
first
X1
X2
mark
X1
mark
from
X
mark
X
true
mark
from
X
mark
X
mark
first
X1
X2
mark
X1
a__first
s
X
cons
Y
Z
mark
Y
mark
from
X
a__from
mark
X
mark
first
X1
X2
mark
X2
mark
s
X
mark
X
a__from
X
mark
X
mark
first
X1
X2
a__first
mark
X1
mark
X2
mark
cons
X1
X2
mark
X1
true
s
1
1
1
a__from
1
1
1
a__first
2
1
2
0
a__from
1
1
2
mark
1
1
0
0
0
29604
from
1
1
2
nil
0
11798
mark
1
1
0
first
2
1
2
1
a__first
2
1
2
1
cons
2
1
2
mark
first
X1
X2
a__first
mark
X1
mark
X2
mark
s
X
s
mark
X
a__first
0
X
nil
a__from
X
cons
mark
X
from
s
X
mark
from
X
a__from
mark
X
a__first
X1
X2
first
X1
X2
mark
nil
nil
a__from
X
from
X
mark
cons
X1
X2
cons
mark
X1
X2
mark
0
0
a__first
s
X
cons
Y
Z
cons
mark
Y
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X
Z
NaTT
certifiable-1.6