10 for y=0 to 14
20 for x=3 to 15 step 6
30 if x+y<=18 then print at y,x+y;"*";at 18-y,x+y;"*"
40 if x-y>=0 then print at y,x-y;"*";at 18-y,x-y;"*"
50 next x:next y