Nontouching List Segments We can define nontouching list segments inductively by: ntlseg c(i,j)der empij ntlseg a-a (i,k)ik jntlseg a (j,k)) or equivalently,we can define them in terms of lseg: ntlseg a(,j）er Iseg a,DAj一 The obvious advantage of knowing that a list segment is non- touching is that it is easy to test whether it is empty: ntlseg a(i,j)→(a=e台i=j) Nontouching List Segments