d+2/9=1-1/9, d+2/9=9/9-1/9, d+2/9=8/9, d=8/9-2/9, d=6/9, d=2/3
f-2/7=7/7-3/7, f-2/7=4,7, f=4/7+2/7, f=6/7
d+2/9=1-1/9, d+2/9=9/9-1/9, d+2/9=8/9, d=8/9-2/9, d=6/9, d=2/3
f-2/7=7/7-3/7, f-2/7=4,7, f=4/7+2/7, f=6/7