Hi Jinsong, it's because the double backslash generates a new voice context for every expression. In fact, the chord where you want to assign the tie, does not exist anymore, because the voice has ended.
See: http://lilypond.org/doc/v2.18/Documentation/notation/multiple-voices.html 'The << {…} \\ {…} >> construct, where the two (or more) expressions are separated by double backslashes, behaves differently to the similar construct without the double backslashes: / all/ the expressions within this construct are assigned to new Voice contexts. These new Voice contexts are created implicitly and are given the fixed names "1", "2", etc.' You could to it this way: \version "2.18.2" \relative c, { \clef "bass" \key g \major \time 3/4 << { \tieNeutral s4 <b' fis'>2 ~ <b fis'>2. ~ | <b fis'>2. } \\ { <b, fis'>2. } >> } Best regards, Martin Am Sonntag, 24. November 2019, 21:56:23 CET schrieb Jinsong Zhao: > \version "2.19.83" > \relative c, { > \clef "bass" > \key g \major > \time 3/4 > << {s4 <b' fis'>2 ~ } \\ {<b, fis'>2.} >> | > <b' fis'>2. ~ | > <b fis'>2. > }
