diff --git a/doc/Builtins.md b/doc/Builtins.md
index dbd31c9..6e55367 100644
--- a/doc/Builtins.md
+++ b/doc/Builtins.md
@@ -1291,9 +1291,9 @@ This function is non-deterministic and automatically vectorized.
 
 __Examples__:
 
-- `4Ṗ` → `[1,1,1,1] [1,1,2] [1,3] [2,2] [4] ...`
+- `4Ṗ` → `[1,1,1,1] [1,1,2] [1,3] [2,2] [4]`
 - `0Ṗ` → `[]`
-- `4_ Ṗ` → ` ...`
+- `4_ Ṗ` → Fail
 - `[2,2]Ṗ` → `[[1,1],[1,1]] [[1,1],[2]] [[2],[1,1]] [[2],[2]]`
 
 ### `sqrt` (`√`, `1 -> 1`)
@@ -1321,7 +1321,7 @@ This function is non-deterministic.
 
 __Examples__:
 
-- `į` → `[0,1] [1,0] ...`
+- `į` → `[0,1] [1,0]`
 
 ### `orNeg` (`ŋ`, `1 -> 1`)
 
@@ -1335,9 +1335,9 @@ When the input is a list, each element is optionally negated independently.
 
 __Examples__:
 
-- `1ŋ` → `1 -1 ...`
-- `0ŋ` → `0 ...`
-- `[-1,2]ŋ` → `[-1,2] [-1,-2] [1,2] [1,-2] ...`
+- `1ŋ` → `1 -1`
+- `0ŋ` → `0`
+- `[-1,2]ŋ` → `[-1,2] [-1,-2] [1,2] [1,-2]`
 
 ### `bitAnd` (`&`, `2 -> 1`)
 
@@ -1347,6 +1347,13 @@ If one or both of the arguments are chars, they are converted to numbers accordi
 
 This function is automatically vectorized and fails when the two lists are of different lengths.
 
+__Examples__:
+
+- `5 3&` → `1`
+- `[5,6] [3,4]&` → `[1,4]`
+- `5 [3,4]&` → `[1,4]`
+- `[5] [3,4]&` → Fail
+
 ### `bitOr` (`|`, `2 -> 1`)
 
 Bitwise OR of two integers.
@@ -1355,6 +1362,13 @@ If one or both of the arguments are chars, they are converted to numbers accordi
 
 This function is automatically vectorized with padding.
 
+__Examples__:
+
+- `5 3|` → `7`
+- `[5,6] [3,4]|` → `[7,6]`
+- `5 [3,4]|` → `[7,5]`
+- `[5] [3,4]|` → `[7,4]`
+
 ### `bitXor` (`X`, `2 -> 1`)
 
 Bitwise XOR of two integers.
@@ -1363,26 +1377,49 @@ If one or both of the arguments are chars, they are converted to numbers accordi
 
 This function is automatically vectorized with padding.
 
+__Examples__:
+
+- `5 3X` → `6`
+- `[5,6] [3,4]X` → `[6,2]`
+- `5 [3,4]X` → `[6,1]`
+- `[5] [3,4]X` → `[6,4]`
+
 ### `popCount` (`Þ`, `1 -> 1`)
 
 Count the number of 1s in the binary digits of an integer.
 
+If the number is smaller than zero, the result is also negated.
+
 If the argument is a char, it is converted to a number according to Nekomata's code page.
 
 This function is automatically vectorized.
 
+__Examples__:
+
+- `13Þ` → `3`
+- `[-13,0,13]Þ` → `[-3,0,3]`
+
 ### `histogram` (`Ħ`, `1 -> 1`)
 
 Compute the histogram of a list of integers.
 
 The result is a list, whose length is the maximum of the input list, and whose nth element is the number of occurrences of n in the input.
 
+Fails when the list contains negative integers or fractions.
+
 If the input is a ragged list, it is flattened before computation.
 
 If the input is a single integer, it is treated as a singleton list.
 
 If the input is a single char, it is converted to a number according to Nekomata's code page, and then treated as a singleton list.
 
+__Examples__:
+
+- `0Ħ` → `[1]`
+- `1Ħ` → `[0,1]`
+- `[1,2,3,2,1]Ħ` → `[0,2,2,1]`
+- `[[1,2],[3,2],[1]]Ħ` → `[0,2,2,1]`
+
 ### `sumEach` (`Ŝ`, `1 -> 1`)
 
 Take the sum of each list in a list of lists of numbers.
@@ -1391,6 +1428,12 @@ The addition is automatically vectorized with padding zeros.
 
 If some of the elements are chars, they are converted to numbers according to Nekomata's code page.
 
+__Examples__:
+
+- `[[1,2],[3,4]]Ŝ` → `[3,7]`
+- `[[1,2],[3,4],[5]]Ŝ` → `[3,7,5]`
+- `[[[1,2],[3,4]],[[5,6],[7,8]]]Ŝ` → `[[4,6],[12,14]]`
+
 ### `charToInt` (`e`, `1 -> 1`)
 
 Convert a char to an integer according to Nekomata's code page.
@@ -1399,6 +1442,11 @@ If the input is already an integer, it is left unchanged.
 
 This function is automatically vectorized.
 
+__Examples__:
+
+- `'a e` → `97`
+- `"Hello"e` → `[72,101,108,108,111]`
+
 ### `intToChar` (`H`, `1 -> 1`)
 
 Convert an integer to a char according to Nekomata's code page.
@@ -1409,16 +1457,32 @@ Fail when the integer is not in the range 0 to 255.
 
 This function is automatically vectorized.
 
+__Examples__:
+
+- `97H` → `'a'`
+- `[72,101,108,108,111]H` → `Hello`
+
 ### `read` (`Ĝ`, `1 -> 1`)
 
 Parse a string (a list of chars) or a single char as a Nekomata value.
 
 Fail when the string is not a valid Nekomata value.
 
+__Examples__:
+
+- `'1 Ĝ` → `1`
+- `"[1,2,3]"Ĝ` → `[1,2,3]`
+
 ### `show` (`ĝ`, `1 -> 1`)
 
 Convert a Nekomata value to a string (a list of chars).
 
+__Examples__:
+
+- `1ĝU` → `["1"]`
+- `[1,2,3]ĝU` → `["[1,2,3]"]`
+- `"Hello"ĝU` → `["\"Hello\""]`
+
 ### `anyOf` (`~`, `1 -> 1`)
 
 Choose an element from a list.
@@ -1427,92 +1491,198 @@ If the argument is a number, it is converted to a range from 0 to that number mi
 
 This function is non-deterministic.
 
+__Examples__:
+
+- `[]~` → Fail
+- `[1,2,3]~` → `1 2 3`
+- `5~` → `0 1 2 3 4`
+
 ### `emptyList` (`Ø`, `0 -> 1`)
 
 Push an empty list.
 
+__Examples__:
+
+- `Ø` → `[]`
+
 ### `singleton` (`U`, `1 -> 1`)
 
 Create a list with a single element.
 
+__Examples__:
+
+- `1U` → `[1]`
+- `[1]U` → `[[1]]`
+
 ### `unsingleton` (`z`, `1 -> 1`)
 
 Get the only element of a list with a single element.
 
 Fails when the list is empty or has more than one element.
 
+__Examples__:
+
+- `[1]z` → `1`
+- `[[1]]z` → `[1]`
+- `[]z` → Fail
+- `[1,2]z` → Fail
+
 ### `pair` (`Ð`, `2 -> 1`)
 
 Create a list with two elements.
 
+__Examples__:
+
+- `1 2Ð` → `[1,2]`
+- `[1] 2Ð` → `[[1],2]`
+
 ### `unpair` (`đ`, `1 -> 2`)
 
 Get the two elements of a list with two elements.
 
 Fails when the length of the list is not 2.
 
+__Examples__:
+
+- `[1,2]đ+` → `3`
+- `[]đ` → Fail
+- `[1]đ` → Fail
+- `[1,2,3]đ` → Fail
+
 ### `removeFail` (`‼`, `1 -> 1`)
 
 Remove failed items from a list.
 
+__Examples__:
+
+- `[1,2,3]‼` → `[1,2,3]`
+- `[1,0,3]P‼` → `[1,3]`
+
 ### `length` (`#`, `1 -> 1`)
 
 Get the length of a list.
 
+__Examples__:
+
+- `[1,2,3]#` → `3`
+- `[]#` → `0`
+
 ### `lengthIs` (`L`, `2 -> 1`)
 
 Check if the length of a list is equal to a given integer.
 
 If it is, push the list itself, otherwise fail.
 
+__Examples__:
+
+- `[1,2,3] 3L` → `[1,2,3]`
+- `[1,2,3] 4L` → Fail
+
 ### `nth` (`@`, `2 -> 1`)
 
 Get the nth element of a list.
 
+The index is 0-based.
+
 This function is automatically vectorized on the second argument.
 
+__Examples__:
+
+- `[1,2,3] 1@` → `2`
+- `[1,2,3] [1,2]@` → `[2,3]`
+
 ### `head` (`h`, `1 -> 1`)
 
 Get the first element of a list.
 
+__Examples__:
+
+- `[1,2,3]h` → `1`
+- `[]h` → Fail
+
 ### `tail` (`t`, `1 -> 1`)
 
 Remove the first element of a list.
 
+__Examples__:
+
+- `[1,2,3]t` → `[2,3]`
+- `[]t` → Fail
+
 ### `cons` (`c`, `2 -> 1`)
 
 Prepend an element to a list.
 
+__Examples__:
+
+- `[2,3] 1c` → `[1,2,3]`
+- `[] 1c` → `[1]`
+
 ### `uncons` (`C`, `1 -> 2`)
 
 Get the first element and the rest of a list.
 
+__Examples__:
+
+- `[1,2,3]CÐ` → `[[2,3],1]`
+- `[]C` → Fail
+
 ### `last` (`l`, `1 -> 1`)
 
 Get the last element of a list.
 
+__Examples__:
+
+- `[1,2,3]l` → `3`
+- `[]l` → Fail
+
 ### `init` (`i`, `1 -> 1`)
 
 Remove the last element of a list.
 
+__Examples__:
+
+- `[1,2,3]i` → `[1,2]`
+- `[]i` → Fail
+
 ### `snoc` (`ɔ`, `2 -> 1`)
 
 Append an element to a list.
 
+__Examples__:
+
+- `[1,2] 3ɔ` → `[1,2,3]`
+- `[] 1ɔ` → `[1]`
+
 ### `unsnoc` (`Ɔ`, `1 -> 2`)
 
 Get the last element and the rest of a list.
 
+__Examples__:
+
+- `[1,2,3]ƆÐ` → `[[1,2],3]`
+- `[]Ɔ` → Fail
+
 ### `cons0` (`ç`, `1 -> 1`)
 
 Prepend a zero to a list.
 
+__Examples__:
+
+- `[1,2,3]ç` → `[0,1,2,3]`
+- `[]ç` → `[0]`
+
 ### `reverse` (`↔`, `1 -> 1`)
 
 Reverse a list.
 
 If the argument is a number, it is converted to a range from 0 to that number minus 1.
 
+__Examples__:
+
+- `[1,2,3]↔` → `[3,2,1]`
+- `3↔` → `[2,1,0]`
+
 ### `prefix` (`p`, `1 -> 1`)
 
 Get a prefix of a list.
@@ -1521,6 +1691,11 @@ If the argument is a number, it is converted to a range from 0 to that number mi
 
 This function is non-deterministic.
 
+__Examples__:
+
+- `[1,2,3]p` → `[] [1] [1,2] [1,2,3]`
+- `3p` → `[] [0] [0,1] [0,1,2]`
+
 ### `suffix` (`s`, `1 -> 1`)
 
 Get a suffix of a list.
@@ -1529,12 +1704,25 @@ If the argument is a number, it is converted to a range from 0 to that number mi
 
 This function is non-deterministic.
 
+__Examples__:
+
+- `[1,2,3]s` → `[1,2,3] [2,3] [3] []`
+- `3s` → `[0,1,2] [1,2] [2] []`
+
 ### `take` (`T`, `2 -> 1`)
 
 Get the first n elements of a list.
 
+Fail when the list is shorter than n.
+
 This function is automatically vectorized on the second argument.
 
+__Examples__:
+
+- `[1,2,3] 2T` → `[1,2]`
+- `[1,2,3] 4T` → Fail
+- `[1,2,3] [2,3]T` → `[[1,2],[1,2,3]]`
+
 ### `subset` (`S`, `1 -> 1`)
 
 Get a finite subset of a list.
@@ -1543,6 +1731,11 @@ If the argument is a number, it is converted to a range from 0 to that number mi
 
 This function is non-deterministic.
 
+__Examples__:
+
+- `[1,2] S` → `[] [1] [2] [1,2]`
+- `2S` → `[] [0] [1] [0,1]`
+
 ### `subsequence` (`q`, `1 -> 1`)
 
 Get a finite contiguous subsequence of a list.
@@ -1551,6 +1744,11 @@ If the argument is a number, it is converted to a range from 0 to that number mi
 
 This function is non-deterministic.
 
+__Examples__:
+
+- `[1,2,3]q` → `[] [1] [1,2] [1,2,3] [2] [2,3] [3]`
+- `3q` → `[] [0] [0,1] [0,1,2] [1] [1,2] [2]`
+
 ### `join` (`,`, `2 -> 1`)
 
 Concatenate two lists.
@@ -1699,6 +1897,8 @@ For each element in the second list, remove the first occurrence of that element
 
 Get the index of any occurrence of an element in a list.
 
+The index is 0-based.
+
 Fail if the element does not occur in the list.
 
 This function is non-deterministic.
diff --git a/src/Nekomata/Builtin.hs b/src/Nekomata/Builtin.hs
index 1945b7d..02afa8c 100644
--- a/src/Nekomata/Builtin.hs
+++ b/src/Nekomata/Builtin.hs
@@ -1199,9 +1199,9 @@ builtins =
         \If the argument is a char, \
         \it is converted to a number according to Nekomata's code page.\n\
         \This function is non-deterministic and automatically vectorized."
-        [ ("4Ṗ", All True ["[1,1,1,1]", "[1,1,2]", "[1,3]", "[2,2]", "[4]"])
+        [ ("4Ṗ", All False ["[1,1,1,1]", "[1,1,2]", "[1,3]", "[2,2]", "[4]"])
         , ("0Ṗ", All False ["[]"])
-        , ("4_ Ṗ", All True [])
+        , ("4_ Ṗ", All False [])
         , ("[2,2]Ṗ", All False ["[[1,1],[1,1]]", "[[1,1],[2]]", "[[2],[1,1]]", "[[2],[2]]"])
         ]
     , Builtin
@@ -1224,7 +1224,7 @@ builtins =
         unitVec2
         "Choose one of [0, 1] and [1, 0] non-deterministically.\n\
         \This function is non-deterministic."
-        [("į", All True ["[0,1]", "[1,0]"])]
+        [("į", All False ["[0,1]", "[1,0]"])]
     , Builtin
         "orNeg"
         'ŋ'
@@ -1235,9 +1235,9 @@ builtins =
         \This function is non-deterministic and automatically vectorized.\n\
         \When the input is a list, \
         \each element is optionally negated independently."
-        [ ("1ŋ", All True ["1", "-1"])
-        , ("0ŋ", All True ["0"])
-        , ("[-1,2]ŋ", All True ["[-1,2]", "[-1,-2]", "[1,2]", "[1,-2]"])
+        [ ("1ŋ", All False ["1", "-1"])
+        , ("0ŋ", All False ["0"])
+        , ("[-1,2]ŋ", All False ["[-1,2]", "[-1,-2]", "[1,2]", "[1,-2]"])
         ]
     , Builtin
         "bitAnd"
@@ -1248,7 +1248,11 @@ builtins =
         \they are converted to numbers according to Nekomata's code page.\n\
         \This function is automatically vectorized \
         \and fails when the two lists are of different lengths."
-        []
+        [ ("5 3&", All False ["1"])
+        , ("[5,6] [3,4]&", All False ["[1,4]"])
+        , ("5 [3,4]&", All False ["[1,4]"])
+        , ("[5] [3,4]&", All False [])
+        ]
     , Builtin
         "bitOr"
         '|'
@@ -1257,7 +1261,11 @@ builtins =
         \If one or both of the arguments are chars, \
         \they are converted to numbers according to Nekomata's code page.\n\
         \This function is automatically vectorized with padding."
-        []
+        [ ("5 3|", All False ["7"])
+        , ("[5,6] [3,4]|", All False ["[7,6]"])
+        , ("5 [3,4]|", All False ["[7,5]"])
+        , ("[5] [3,4]|", All False ["[7,4]"])
+        ]
     , Builtin
         "bitXor"
         'X'
@@ -1266,16 +1274,23 @@ builtins =
         \If one or both of the arguments are chars, \
         \they are converted to numbers according to Nekomata's code page.\n\
         \This function is automatically vectorized with padding."
-        []
+        [ ("5 3X", All False ["6"])
+        , ("[5,6] [3,4]X", All False ["[6,2]"])
+        , ("5 [3,4]X", All False ["[6,1]"])
+        , ("[5] [3,4]X", All False ["[6,4]"])
+        ]
     , Builtin
         "popCount"
         'Þ'
         popCount'
         "Count the number of 1s in the binary digits of an integer.\n\
+        \If the number is smaller than zero, the result is also negated.\n\
         \If the argument is a char, \
         \it is converted to a number according to Nekomata's code page.\n\
         \This function is automatically vectorized."
-        []
+        [ ("13Þ", All False ["3"])
+        , ("[-13,0,13]Þ", All False ["[-3,0,3]"])
+        ]
     , Builtin
         "histogram"
         'Ħ'
@@ -1285,6 +1300,7 @@ builtins =
         \whose length is the maximum of the input list, \
         \and whose nth element is the number of occurrences \
         \of n in the input.\n\
+        \Fails when the list contains negative integers or fractions.\n\
         \If the input is a ragged list, \
         \it is flattened before computation.\n\
         \If the input is a single integer, \
@@ -1292,7 +1308,11 @@ builtins =
         \If the input is a single char, \
         \it is converted to a number according to Nekomata's code page, \
         \and then treated as a singleton list."
-        []
+        [ ("0Ħ", All False ["[1]"])
+        , ("1Ħ", All False ["[0,1]"])
+        , ("[1,2,3,2,1]Ħ", All False ["[0,2,2,1]"])
+        , ("[[1,2],[3,2],[1]]Ħ", All False ["[0,2,2,1]"])
+        ]
     , Builtin
         "sumEach"
         'Ŝ'
@@ -1301,7 +1321,10 @@ builtins =
         \The addition is automatically vectorized with padding zeros.\n\
         \If some of the elements are chars, \
         \they are converted to numbers according to Nekomata's code page."
-        []
+        [ ("[[1,2],[3,4]]Ŝ", All False ["[3,7]"])
+        , ("[[1,2],[3,4],[5]]Ŝ", All False ["[3,7,5]"])
+        , ("[[[1,2],[3,4]],[[5,6],[7,8]]]Ŝ", All False ["[[4,6],[12,14]]"])
+        ]
     , Builtin
         "charToInt"
         'e'
@@ -1309,7 +1332,9 @@ builtins =
         "Convert a char to an integer according to Nekomata's code page.\n\
         \If the input is already an integer, it is left unchanged.\n\
         \This function is automatically vectorized."
-        []
+        [ ("'a e", All False ["97"])
+        , ("\"Hello\"e", All False ["[72,101,108,108,111]"])
+        ]
     , Builtin
         "intToChar"
         'H'
@@ -1318,7 +1343,9 @@ builtins =
         \If the input is already a char, it is left unchanged.\n\
         \Fail when the integer is not in the range 0 to 255.\n\
         \This function is automatically vectorized."
-        []
+        [ ("97H", All False ["'a'"])
+        , ("[72,101,108,108,111]H", All False ["Hello"])
+        ]
     , Builtin
         "read"
         'Ĝ'
@@ -1326,13 +1353,18 @@ builtins =
         "Parse a string (a list of chars) or a single char \
         \as a Nekomata value.\n\
         \Fail when the string is not a valid Nekomata value."
-        []
+        [ ("'1 Ĝ", All False ["1"])
+        , ("\"[1,2,3]\"Ĝ", All False ["[1,2,3]"])
+        ]
     , Builtin
         "show"
         'ĝ'
         show'
         "Convert a Nekomata value to a string (a list of chars)."
-        []
+        [ ("1ĝU", All False ["[\"1\"]"])
+        , ("[1,2,3]ĝU", All False ["[\"[1,2,3]\"]"])
+        , ("\"Hello\"ĝU", All False ["[\"\\\"Hello\\\"\"]"])
+        ]
     , Builtin
         "anyOf"
         '~'
@@ -1341,119 +1373,161 @@ builtins =
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1.\n\
         \This function is non-deterministic."
-        []
+        [ ("[]~", All False [])
+        , ("[1,2,3]~", All False ["1", "2", "3"])
+        , ("5~", All False ["0", "1", "2", "3", "4"])
+        ]
     , Builtin
         "emptyList"
         'Ø'
         emptyList
         "Push an empty list."
-        []
+        [("Ø", All False ["[]"])]
     , Builtin
         "singleton"
         'U'
         singleton'
         "Create a list with a single element."
-        []
+        [ ("1U", All False ["[1]"])
+        , ("[1]U", All False ["[[1]]"])
+        ]
     , Builtin
         "unsingleton"
         'z'
         unsingleton
         "Get the only element of a list with a single element.\n\
         \Fails when the list is empty or has more than one element."
-        []
+        [ ("[1]z", All False ["1"])
+        , ("[[1]]z", All False ["[1]"])
+        , ("[]z", All False [])
+        , ("[1,2]z", All False [])
+        ]
     , Builtin
         "pair"
         'Ð'
         pair
         "Create a list with two elements."
-        []
+        [ ("1 2Ð", All False ["[1,2]"])
+        , ("[1] 2Ð", All False ["[[1],2]"])
+        ]
     , Builtin
         "unpair"
         'đ'
         unpair
         "Get the two elements of a list with two elements.\n\
         \Fails when the length of the list is not 2."
-        []
+        [ ("[1,2]đ+", All False ["3"])
+        , ("[]đ", All False [])
+        , ("[1]đ", All False [])
+        , ("[1,2,3]đ", All False [])
+        ]
     , Builtin
         "removeFail"
         '‼'
         removeFail
         "Remove failed items from a list."
-        []
+        [ ("[1,2,3]‼", All False ["[1,2,3]"])
+        , ("[1,0,3]P‼", All False ["[1,3]"])
+        ]
     , Builtin
         "length"
         '#'
         length'
         "Get the length of a list."
-        []
+        [ ("[1,2,3]#", All False ["3"])
+        , ("[]#", All False ["0"])
+        ]
     , Builtin
         "lengthIs"
         'L'
         lengthIs
         "Check if the length of a list is equal to a given integer.\n\
         \If it is, push the list itself, otherwise fail."
-        []
+        [ ("[1,2,3] 3L", All False ["[1,2,3]"])
+        , ("[1,2,3] 4L", All False [])
+        ]
     , Builtin
         "nth"
         '@'
         nth
         "Get the nth element of a list.\n\
+        \The index is 0-based.\n\
         \This function is automatically vectorized on the second argument."
-        []
+        [ ("[1,2,3] 1@", All False ["2"])
+        , ("[1,2,3] [1,2]@", All False ["[2,3]"])
+        ]
     , Builtin
         "head"
         'h'
         head'
         "Get the first element of a list."
-        []
+        [ ("[1,2,3]h", All False ["1"])
+        , ("[]h", All False [])
+        ]
     , Builtin
         "tail"
         't'
         tail'
         "Remove the first element of a list."
-        []
+        [ ("[1,2,3]t", All False ["[2,3]"])
+        , ("[]t", All False [])
+        ]
     , Builtin
         "cons"
         'c'
         cons
         "Prepend an element to a list."
-        []
+        [ ("[2,3] 1c", All False ["[1,2,3]"])
+        , ("[] 1c", All False ["[1]"])
+        ]
     , Builtin
         "uncons"
         'C'
         uncons
         "Get the first element and the rest of a list."
-        []
+        [ ("[1,2,3]CÐ", All False ["[[2,3],1]"])
+        , ("[]C", All False [])
+        ]
     , Builtin
         "last"
         'l'
         last'
         "Get the last element of a list."
-        []
+        [ ("[1,2,3]l", All False ["3"])
+        , ("[]l", All False [])
+        ]
     , Builtin
         "init"
         'i'
         init'
         "Remove the last element of a list."
-        []
+        [ ("[1,2,3]i", All False ["[1,2]"])
+        , ("[]i", All False [])
+        ]
     , Builtin
         "snoc"
         'ɔ'
         snoc
         "Append an element to a list."
-        []
+        [ ("[1,2] 3ɔ", All False ["[1,2,3]"])
+        , ("[] 1ɔ", All False ["[1]"])
+        ]
     , Builtin
         "unsnoc"
         'Ɔ'
         unsnoc
         "Get the last element and the rest of a list."
-        []
+        [ ("[1,2,3]ƆÐ", All False ["[[1,2],3]"])
+        , ("[]Ɔ", All False [])
+        ]
     , Builtin
         "cons0"
         'ç'
         cons0
         "Prepend a zero to a list."
-        []
+        [ ("[1,2,3]ç", All False ["[0,1,2,3]"])
+        , ("[]ç", All False ["[0]"])
+        ]
     , Builtin
         "reverse"
         '↔'
@@ -1461,7 +1535,9 @@ builtins =
         "Reverse a list.\n\
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1."
-        []
+        [ ("[1,2,3]↔", All False ["[3,2,1]"])
+        , ("3↔", All False ["[2,1,0]"])
+        ]
     , Builtin
         "prefix"
         'p'
@@ -1470,7 +1546,9 @@ builtins =
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1.\n\
         \This function is non-deterministic."
-        []
+        [ ("[1,2,3]p", All False ["[]", "[1]", "[1,2]", "[1,2,3]"])
+        , ("3p", All False ["[]", "[0]", "[0,1]", "[0,1,2]"])
+        ]
     , Builtin
         "suffix"
         's'
@@ -1479,14 +1557,20 @@ builtins =
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1.\n\
         \This function is non-deterministic."
-        []
+        [ ("[1,2,3]s", All False ["[1,2,3]", "[2,3]", "[3]", "[]"])
+        , ("3s", All False ["[0,1,2]", "[1,2]", "[2]", "[]"])
+        ]
     , Builtin
         "take"
         'T'
         take'
         "Get the first n elements of a list.\n\
+        \Fail when the list is shorter than n.\n\
         \This function is automatically vectorized on the second argument."
-        []
+        [ ("[1,2,3] 2T", All False ["[1,2]"])
+        , ("[1,2,3] 4T", All False [])
+        , ("[1,2,3] [2,3]T", All False ["[[1,2],[1,2,3]]"])
+        ]
     , Builtin
         "subset"
         'S'
@@ -1495,7 +1579,9 @@ builtins =
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1.\n\
         \This function is non-deterministic."
-        []
+        [ ("[1,2] S", All False ["[]", "[1]", "[2]", "[1,2]"])
+        , ("2S", All False ["[]", "[0]", "[1]", "[0,1]"])
+        ]
     , Builtin
         "subsequence"
         'q'
@@ -1504,7 +1590,9 @@ builtins =
         \If the argument is a number, \
         \it is converted to a range from 0 to that number minus 1.\n\
         \This function is non-deterministic."
-        []
+        [ ("[1,2,3]q", All False ["[]", "[1]", "[1,2]", "[1,2,3]", "[2]", "[2,3]", "[3]"])
+        , ("3q", All False ["[]", "[0]", "[0,1]", "[0,1,2]", "[1]", "[1,2]", "[2]"])
+        ]
     , Builtin
         "join"
         ','
@@ -1680,6 +1768,7 @@ builtins =
         'Ĩ'
         index
         "Get the index of any occurrence of an element in a list.\n\
+        \The index is 0-based.\n\
         \Fail if the element does not occur in the list.\n\
         \This function is non-deterministic."
         []