level=0         a=1  		b=1
level=1         a=0.5,0.5	b=1
level=1         a=1  		b=0.5,0.5
level=2         a=0.75,0.25	b=1
level=2         a=1  		b=0.75,0.25
level=3         a=0.5,0.5	b=0.5,0.5
level=4         a=0.75,0.25	b=0.5,0.5
level=4         a=0.5,0.5	b=0.75,0.25
level=4         a=0.75,0.25	b=0.75,0.25