first
0
X
nil
first
s
X
cons
Y
Z
cons
Y
n__first
X
activate
Z
from
X
cons
X
n__from
s
X
first
X1
X2
n__first
X1
X2
from
X
n__from
X
activate
n__first
X1
X2
first
X1
X2
activate
n__from
X
from
X
activate
X
X
first
2
0
0
nil
0
s
1
cons
2
n__first
2
activate
1
from
1
n__from
1
FULL