(define (append! x y)
  (set-cdr! (last-pair x) y)
  x)

(define (last-pair x)
  (if (null? (cdr x))
      x
      (last-pair (cdr x))))

(define x (list 'a 'b))
(define y (list 'c 'd))

;; Append takes two cons cells (sorta like lists/arrays, 
;;but not really, but lists
;; which are used here allow you to do 
;;cons-cell stuff to it by default)
;; takes the pairs of x and y (pair is really n-items)
;; and appends x to y, 
;;thus ('a 'b 'c) & ('e 'f 'g) => ('a 'b 'c 'd 'e 'f)

;; now create append! which takes two cons x y
;; and appends them together, thus ('a 'b 'c) & ('e 'f 'g) => ('a 'b 'c 'd 'e 'f)
(define (append! x y)
  (set-cdr! (last-pair x) y)
  x)

;; last pair is a helper function to append! 
;;(append is a tail-recursive function)
;; which uses tail recursion to create a single list. 
;; look back up to (append!) and notice 
;;(set-cdr!(....)), which is a procedure
;; that takes the list (in this case) 
;;of x and creates a mutated list.
(define (last-pair x)
  (if (null? (cdr x))
      x
      (last-pair (cdr x))))

;; This of course creates two global variables x and y
(define x (list 'a 'b))
(define y (list 'c 'd))

> (car x)
'a
> (cdr x)
(mcons 'b '())
> (car y)
'c
> (cdr y)
(mcons 'd '())

> (define z (append x y))
> z
(mcons 'a (mcons 'b (mcons 'c (mcons 'd '()))))
> (car x)
'a
> (cdr x)
(mcons 'b '())
> (car y)
'c
> (cdr y)
(mcons 'd '())
>

> (define w (append! x y))
> w
(mcons 'a (mcons 'b (mcons 'c (mcons 'd '()))))
> (car x)
'a
> (cdr x)
(mcons 'b (mcons 'c (mcons 'd '())))
> (car y)
'c
> (cdr y)
(mcons 'd '())

CREATE TABLE Games 
(gameid INTEGER PRIMARY KEY, 
homeid INTEGER, 
awayid INTEGER);

CREATE TABLE TeamStats 
(gameid INTEGER, 
teamid INTEGER, 
PRIMARY KEY (gameid, teamid));

DELETE t FROM TeamStats AS t 
JOIN Games AS g 
ON 
g.gameid = t.gameid 
AND g.homeid != t.teamid 
AND g.awayid != t.teamid;

DELETE FROM TeamStats 
WHERE CAST(gameid AS TEXT) 
|| "," 
|| CAST(teamid AS TEXT) 
IN 
(SELECT CAST(t.gameid AS TEXT) 
|| "," 
|| CAST(t.teamid AS TEXT) 
FROM TeamStats AS t 
JOIN Games AS g 
ON 
g.gameid = t.gameid 
AND 
g.homeid != t.teamid 
AND 
g.awayid != t.teamid);