Q2 := (x - 1) (x + 1) (y - 1) (y + 1)
Q1 := (x + y + 3) (x + y - 3) (-x + y + 3) (-x + y - 3)
Q := (x - 4) (x - 1) (x + 1) (y - 1)
> # I 16 punti di intersezione di Q1, Q2: 
> R:={solve({Q1=0, Q2=0}, {x,y})};
 y = 2, x = -1
 y = 4, x = -1
 y = 4, x = 1
 y = 2, x = 1
 y = -1, x = 4
 y = 1, x = -2
 y = 1, x = -4
 y = 1, x = 4
 y = 1, x = 2
 x = 1, y = -2
 x = 1, y = -4
 x = -1, y = -2
 x = -1, y = -4
 ---
 y = -1, x = -4
 y = -1, x = 2
 y = -1, x = -2
> S:={solve({Q1=0, Q=0}, {x,y})};
 y = 2, x = -1
 y = 4, x = -1
 y = 4, x = 1
 y = 2, x = 1
 y = -1, x = 4
 y = 1, x = -2
 y = 1, x = -4
 y = 1, x = 4
 y = 1, x = 2
 x = 1, y = -2
 x = 1, y = -4
 x = -1, y = -2
 x = -1, y = -4
 ---
 x = 4, y = 7
 x = 4, y = -7
> R intersect S
Warning, inserted missing semicolon at end of statement, ...R intersect S;
{{y = 2, x = -1}, {x = -1, y = -2}, {x = -1, y = -4}, {y = 4, x = -1}, 

  {y = 4, x = 1}, {y = 2, x = 1}, {x = 1, y = -2}, {x = 1, y = -4}, 

  {y = -1, x = 4}, {y = 1, x = -2}, {y = 1, x = -4}, {y = 1, x = 4}, 

  {y = 1, x = 2}}
> S minus R
Warning, inserted missing semicolon at end of statement, S minus R;
               {{x = 4, y = 7}, {x = 4, y = -7}}
> R minus S
Warning, inserted missing semicolon at end of statement, R minus S;
     {{y = -1, x = -2}, {y = -1, x = -4}, {y = -1, x = 2}}