ffc ffb ffa
fdg feg ffg
lxyz nxyz mxyz
{abc,def}
{abc}
{a,b,c,d,e}
x} y} {a} b} c}
x,y {abc} trie
/usr/ucb/ex /usr/ucb/edit /usr/lib/ex /usr/lib/how_ex
XXXX{a,b,c}
XXXXa XXXXb XXXXc
{}
{ }
}
{
abcd{efgh