10REM FOURPNT / DRAWS A PATTERN WITH 4 POINTS
   20REM JOHN A COLL
   30REM VERSION 1 / 16 NOV 81
   40REM MODEL A
   50MODE 4
   60VDU 29,640;512;
   80FOR A=0 TO 500 STEP 15
   90MOVE A-500,0
  100DRAW 0,A
  110DRAW 500-A,0
  120DRAW 0,-A
  130DRAW A-500,0
  140NEXT A
  160FOR B=0 TO 7 :REM Change the color
  170FOR C=1 TO 3
  180T=TIME :REM Wait a while
  190REPEAT UNTIL TIME-T>50
  200VDU 19,3,C,0,0,0
  210VDU 19,0,6,0,0,0
  220NEXT C
  230NEXT B