COUNT.html -- ACL2 Version 6.3

### COUNT

count the number of occurrences of an item in a string or true-list

    Major Section:  ACL2-BUILT-INS

    Example Forms:
    (count #\D "DabcDefcDe")                 ; = 3
    (count #\D "DabcDefcDe" :start 1)        ; = 2
    (count #\D "DabcDefcDe" :start 1 :end 5) ; = 1
    (count #\D "DabcDefcDe" :start 1 :end 4) ; = 0
    (count #\z "DabcDefcDe")                 ; = 0
    (count '(a b) '(17 (a b) 23 (a b) (c d)))   ; = 2

    General Form:
    (count item sequence &key start end)

`(Count item sequence)` returns the number of times `item` occurs in `sequence`. The guard for calls of `count` (which is actually a macro in ACL2) specifies that `sequence` is a string or a true-list, and that `start`, which defaults to 0, and `end`, which defaults to the length of `sequence`, are valid indices into sequence.

See any Common Lisp documentation for more information about `count`, which is a Common Lisp utility. At this time ACL2 does not support keyword arguments for `count` other than `:start` and `:end`; we may add support for the `:from-end` keyword upon request.