{ }
a {r1r2}
b {r1r3}
c
{r1r2r3}
d {r2r4}
ab
{r1}
ac {r1r2}
ad {r2}
abc
{r1}
abd { }
acd { r2}
bc {r1r3}
bd
{ }
bcd
{ }
cd
{r2 }
{ }
r1 {abc}
r2 {acd}
r3 {bc}
r4{d}
r1r2 {ac}
r1r3 {bc}
r1r4 { }
r1r2r3 {c}
r1r2r4 { }
r1r3r4 { }
r2r3 {c}
r2r4{d }
r2r3r4 { }
r3r4
{ }
Single
Enumeration Tree
r1r2r3r4 { }
abcd
{ }
Feature
enumeration
Row enumeration