Dynamic
Enumeration Tree
{ }
a {r1r2}
b {r1r3}
c
{r1r2r3}
d {r2r4}
r1
{bc}
r2 {cd}
r1r2
{c}
r1
{c}
r3
{ c}
r1r3
{ c}
r2
{d }
Feature enumeration to Row enumeration
ab
{r1}
ac {r1r2}
ad
{r2}
abc
{r1}
abd
{ }
acd
{ r2}
abcd
{ }
a {r1r2}
abc:
{r1}
ac:
{r1r2}
acd:
{r2}