digraph G {
"{X, Y, Z}" -> "{X, Y}" 
"{X, Y, Z}" -> "{X, Z}" 
"{X, Y, Z}" -> "{Y, Z}" 

"{X, Y}" -> "{X}"
"{X, Y}" -> "{Y}"

"{X, Z}" -> "{X}"
"{X, Z}" -> "{Z}"

"{Y, Z}" -> "{Y}"
"{Y, Z}" -> "{Z}"

"{X}" -> "{}"
"{Y}" -> "{}"
"{Z}" -> "{}"
}