100 REM Mandelbrot Set in B & W
110 HGR:POKE 49234,0:HCOLOR=3
120 FOR x = 0 TO 279:FOR y = 0 TO 95
130 x1 = x / 280 * 3 - 2:y1 = y / 191 * 2 - 1
140 i = 0:s = x1:t = y1:c = 0
150 s1 = s * s - t * t + x1
160 t = 2 * s * t + y1:s = s1:c = 1 - c:i = i + 1
170 IF s * s + t * t < 4 AND i < 117 THEN GOTO 150
180 IF c = 0 THEN HPLOT x,y:HPLOT x,191 - y
190 NEXT:NEXT