[1.0]
head: 1.0
tail: []
length: 1
at index0 0: 1.0
at index0 1: _
at index0 2: _
at index0 3: _
at index0 4: _
at index0 7: _
at index0 8: _
at index0 9: _
at index0 14: _
at index0 15: _
at index0 16: _
drop 0: [1.0]
drop 1: []
drop 2: failed
drop 5: failed
drop 9: failed

[2.0, 1.0]
head: 2.0
tail: [1.0]
length: 2
at index0 0: 2.0
at index0 1: 1.0
at index0 2: _
at index0 3: _
at index0 4: _
at index0 7: _
at index0 8: _
at index0 9: _
at index0 14: _
at index0 15: _
at index0 16: _
drop 0: [2.0, 1.0]
drop 1: [1.0]
drop 2: []
drop 5: failed
drop 9: failed

[3.0, 2.0, 1.0]
head: 3.0
tail: [2.0, 1.0]
length: 3
at index0 0: 3.0
at index0 1: 2.0
at index0 2: 1.0
at index0 3: _
at index0 4: _
at index0 7: _
at index0 8: _
at index0 9: _
at index0 14: _
at index0 15: _
at index0 16: _
drop 0: [3.0, 2.0, 1.0]
drop 1: [2.0, 1.0]
drop 2: [1.0]
drop 5: failed
drop 9: failed

[4.0, 3.0, 2.0, 1.0]
head: 4.0
tail: [3.0, 2.0, 1.0]
length: 4
at index0 0: 4.0
at index0 1: 3.0
at index0 2: 2.0
at index0 3: 1.0
at index0 4: _
at index0 7: _
at index0 8: _
at index0 9: _
at index0 14: _
at index0 15: _
at index0 16: _
drop 0: [4.0, 3.0, 2.0, 1.0]
drop 1: [3.0, 2.0, 1.0]
drop 2: [2.0, 1.0]
drop 5: failed
drop 9: failed

[4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
head: 4.0
tail: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
length: 8
at index0 0: 4.0
at index0 1: 3.0
at index0 2: 2.0
at index0 3: 1.0
at index0 4: 4.0
at index0 7: 1.0
at index0 8: _
at index0 9: _
at index0 14: _
at index0 15: _
at index0 16: _
drop 0: [4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 1: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 2: [2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 5: [3.0, 2.0, 1.0]
drop 9: failed

[4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
head: 4.0
tail: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
length: 16
at index0 0: 4.0
at index0 1: 3.0
at index0 2: 2.0
at index0 3: 1.0
at index0 4: 4.0
at index0 7: 1.0
at index0 8: 4.0
at index0 9: 3.0
at index0 14: 2.0
at index0 15: 1.0
at index0 16: _
drop 0: [4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 1: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 2: [2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 5: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]
drop 9: [3.0, 2.0, 1.0, 4.0, 3.0, 2.0, 1.0]

foldl (should be 10 to 1):
"<ten>"
"<nine>"
"<eight>"
"<seven>"
"<six>"
"<five>"
"<four>"
"<three>"
"<two>"
"<one>"

foldr (should be 1 to 10):
"<one><two><three><four><five><six><seven><eight><nine><ten>"

construction 1
cons(1, leaf("one"), nil)
cons(1, leaf("one"), nil)

construction 2
cons(1, leaf("one"), nil)
cons(1, leaf("one"), cons(1, leaf("two"), nil))

construction 3
cons(3, node("one", leaf("two"), leaf("three")), nil)
cons(3, node("one", leaf("two"), leaf("three")), nil)

construction 4
cons(1, leaf("one"), cons(3, node("two", leaf("three"), leaf("four")), nil))
cons(1, leaf("one"), cons(3, node("two", leaf("three"), leaf("four")), nil))

construction 5
cons(1, leaf("one"), cons(3, node("three", leaf("four"), leaf("five")), nil))
cons(1, leaf("one"), cons(1, leaf("two"), cons(3, node("three", leaf("four"), leaf("five")), nil)))

construction 6
cons(3, node("one", leaf("two"), leaf("three")), nil)
cons(3, node("one", leaf("two"), leaf("three")), cons(3, node("four", leaf("five"), leaf("six")), nil))

construction 7
cons(7, node("one", node("two", leaf("three"), leaf("four")), node("five", leaf("six"), leaf("seven"))), nil)
cons(7, node("one", node("two", leaf("three"), leaf("four")), node("five", leaf("six"), leaf("seven"))), nil)

construction 8
cons(1, leaf("one"), cons(7, node("two", node("three", leaf("four"), leaf("five")), node("six", leaf("seven"), leaf("eight"))), nil))
cons(1, leaf("one"), cons(7, node("two", node("three", leaf("four"), leaf("five")), node("six", leaf("seven"), leaf("eight"))), nil))

construction 9
cons(1, leaf("one"), cons(7, node("three", node("four", leaf("five"), leaf("six")), node("seven", leaf("eight"), leaf("nine"))), nil))
cons(1, leaf("one"), cons(1, leaf("two"), cons(7, node("three", node("four", leaf("five"), leaf("six")), node("seven", leaf("eight"), leaf("nine"))), nil)))

construction 10
cons(3, node("one", leaf("two"), leaf("three")), cons(7, node("four", node("five", leaf("six"), leaf("seven")), node("eight", leaf("nine"), leaf("ten"))), nil))
cons(3, node("one", leaf("two"), leaf("three")), cons(7, node("four", node("five", leaf("six"), leaf("seven")), node("eight", leaf("nine"), leaf("ten"))), nil))

construction 11
cons(1, leaf("one"), cons(3, node("two", leaf("three"), leaf("four")), cons(7, node("five", node("six", leaf("seven"), leaf("eight")), node("nine", leaf("ten"), leaf("eleven"))), nil)))
cons(1, leaf("one"), cons(3, node("two", leaf("three"), leaf("four")), cons(7, node("five", node("six", leaf("seven"), leaf("eight")), node("nine", leaf("ten"), leaf("eleven"))), nil)))

construction 12
cons(1, leaf("one"), cons(3, node("three", leaf("four"), leaf("five")), cons(7, node("six", node("seven", leaf("eight"), leaf("nine")), node("ten", leaf("eleven"), leaf("twelve"))), nil)))
cons(1, leaf("one"), cons(1, leaf("two"), cons(3, node("three", leaf("four"), leaf("five")), cons(7, node("six", node("seven", leaf("eight"), leaf("nine")), node("ten", leaf("eleven"), leaf("twelve"))), nil))))

construction 13
cons(3, node("one", leaf("two"), leaf("three")), cons(7, node("seven", node("eight", leaf("nine"), leaf("ten")), node("eleven", leaf("twelve"), leaf("thirteen"))), nil))
cons(3, node("one", leaf("two"), leaf("three")), cons(3, node("four", leaf("five"), leaf("six")), cons(7, node("seven", node("eight", leaf("nine"), leaf("ten")), node("eleven", leaf("twelve"), leaf("thirteen"))), nil)))

construction 14
cons(7, node("one", node("two", leaf("three"), leaf("four")), node("five", leaf("six"), leaf("seven"))), nil)
cons(7, node("one", node("two", leaf("three"), leaf("four")), node("five", leaf("six"), leaf("seven"))), cons(7, node("eight", node("nine", leaf("ten"), leaf("eleven")), node("twelve", leaf("thirteen"), leaf("fourteen"))), nil))

construction 15
cons(15, node("one", node("two", node("three", leaf("four"), leaf("five")), node("six", leaf("seven"), leaf("eight"))), node("nine", node("ten", leaf("eleven"), leaf("twelve")), node("thirteen", leaf("fourteen"), leaf("fifteen")))), nil)
cons(15, node("one", node("two", node("three", leaf("four"), leaf("five")), node("six", leaf("seven"), leaf("eight"))), node("nine", node("ten", leaf("eleven"), leaf("twelve")), node("thirteen", leaf("fourteen"), leaf("fifteen")))), nil)

construction 16
cons(1, leaf("one"), cons(15, node("two", node("three", node("four", leaf("five"), leaf("six")), node("seven", leaf("eight"), leaf("nine"))), node("ten", node("eleven", leaf("twelve"), leaf("thirteen")), node("fourteen", leaf("fifteen"), leaf("sixteen")))), nil))
cons(1, leaf("one"), cons(15, node("two", node("three", node("four", leaf("five"), leaf("six")), node("seven", leaf("eight"), leaf("nine"))), node("ten", node("eleven", leaf("twelve"), leaf("thirteen")), node("fourteen", leaf("fifteen"), leaf("sixteen")))), nil))

construction 17
cons(1, leaf("one"), cons(15, node("three", node("four", node("five", leaf("six"), leaf("seven")), node("eight", leaf("nine"), leaf("ten"))), node("eleven", node("twelve", leaf("thirteen"), leaf("fourteen")), node("fifteen", leaf("sixteen"), leaf("seventeen")))), nil))
cons(1, leaf("one"), cons(1, leaf("two"), cons(15, node("three", node("four", node("five", leaf("six"), leaf("seven")), node("eight", leaf("nine"), leaf("ten"))), node("eleven", node("twelve", leaf("thirteen"), leaf("fourteen")), node("fifteen", leaf("sixteen"), leaf("seventeen")))), nil)))