Single Enumeration Tree

abcd  { }

r1r2r3r4 { }

abc  {r1}

r1r2r3 {c}

r1r2 {ac}

ab {r1}

abd { }

r1r2r4 { }

a {r1r2}

ac {r1r2}

acd { r2}

r1 {abc}

r1r3 {bc}

r1r3r4 { }

ad {r2}

r1r4 { }

bc {r1r3}

r2r3r4 { }

bcd { }

r2r3 {c}

{ }

b {r1r3}

r2 {acd}

{ }

r2r4{d }

bd { }

c {r1r2r3}

cd  {r2 }

r3r4 { }

r3 {bc}

d {r2r4}

r4{d}

Feature enumeration

Row enumeration