- lset-adjoin = list elt_1 ...procedure
Adds the ELT_I elements not already in the list parameter to the result list. The result shares a common tail with the list parameter. The new elements are added to the front of the list, but no guarantees are made about their order. The = parameter is an equality procedure used to determine if an ELT_I is already a member of LIST. Its first argument is an element of LIST; its second is one of the ELT_I.
The list parameter is always a suffix of the result -- even if the list parameter contains repeated elements, these are not reduced.
(lset-adjoin eq? '(a b c d c e) 'a 'e 'i 'o 'u) => (u o i a b c d c e)