(@ factorial n +-                                                    factorial = n ->
    ({*} 1..n)                                                         [*] {1..n}
)                                                                    ;
(@ factorial n +-
    1                                                                factorial = n ->
+                                                                      1
    [= 0] n                                                          _
)                                                                      n = 0
                                                                     ;













