Scheme PHP [Source Code]
rember 
function rember
($s, $l)
{return
    is_nulll($l) ? [] 
    : (is_eq(car($l), $s) ? cdr($l) 
      : cons(car($l), rember($s, cdr($l))));
}
firsts 
function firsts
($l)
{return
    is_nulll($l) ? [] 
    : cons(car(car($l)), firsts(cdr($l)));
}
insertR 
function insert_right
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ? cons($old_s, cons($new_s, cdr($l)))
      : cons(car($l), insert_right($new_s, $old_s, cdr($l))));
}
insertL 
function insert_left
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ? cons($new_s, $l)
      : cons(car($l), insert_left($new_s, $old_s, cdr($l))));
}
subst 
function subst
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ? cons($new_s, cdr($l))
      : cons(car($l), subst($new_s, $old_s, cdr($l))));
}
subst2 
function subst2
($new_s, $old_s1, $old_s2, $l)
{return 
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s1) || is_eq(car($l), $old_s2) ? 
        cons($new_s, cdr($l))
      : cons(car($l), subst2($new_s, $old_s1, $old_s2, cdr($l))));
}
multirember 
function multirember
($s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $s) ? multirember($s, cdr($l))
      : cons(car($l), multirember($s, cdr($l))));
}
multiinsertR 
function multiinsert_right
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ? 
        cons($old_s, 
             cons($new_s, 
                    multiinsert_right($new_s, $old_s, cdr($l))))
      : cons(car($l), multiinsert_right($new_s, $old_s, cdr($l))));
}
multiinsertL 
function multiinsert_left
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ?
            cons($new_s,
                 cons($old_s,
                    multiinsert_left($new_s, $old_s, cdr($l))))
      : cons(car($l), multiinsert_left($new_s, $old_s, cdr($l))));
}
multisubst 
function multisubst
($new_s, $old_s, $l)
{return
    is_nulll($l) ? []
    : (is_eq(car($l), $old_s) ?
       cons($new_s, multisubst($new_s, $old_s, cdr($l)))
      : cons(car($l), multisubst($new_s, $old_s, cdr($l))));
}