DELETE-ASSOC.html -- ACL2 Version 6.3

### DELETE-ASSOC

remove the first pair from an association list for a given key

    Major Section:  ACL2-BUILT-INS

    General Forms:
    (delete-assoc key alist)
    (delete-assoc key alist :test 'eql)   ; same as above (eql as equality test)
    (delete-assoc key alist :test 'eq)    ; same, but eq is equality test
    (delete-assoc key alist :test 'equal) ; same, but equal is equality test

`(Delete-assoc key alist)` returns an alist that is the same as the list `alist`, except that the first pair in `alist` with a `car` of `key` is deleted, if there is one; otherwise `alist` is returned. Note that the order of the elements of `alist` is unchanged (though one may be deleted).

The guard for a call of `delete-assoc` depends on the test. In all cases, the second argument must satisfy `alistp`. If the test is `eql`, then either the first argument must be suitable for `eql` (see eqlablep) or the second argument must satisfy `eqlable-alistp`. If the test is `eq`, then either the first argument must be a symbol or the second argument must satisfy `symbol-alistp`.

See equality-variants for a discussion of the relation between `delete-assoc` and its variants:

> `(delete-assoc-eq key alist)` is equivalent to `(delete-assoc key alist :test 'eq)`;

> `(delete-assoc-equal key alist)` is equivalent to `(delete-assoc key alist :test 'equal)`.

In particular, reasoning about any of these primitives reduces to reasoning about the function `delete-assoc-equal`.