How to tie a flat to g sharp

[Kilian A. Foth]

Greetings,

I am having a hard time convincing Lilypond to create a tie between
enharmonic variants:

\version "2.4.0"

\score {
  \new PianoStaff << 
    \new Staff { 
      \time 4/4 \key des \major
      \relative c'' {
        <es as c es>4\arpeggio des'8 c 
        << { <c es ges as>2 } \\ { \grace{bes16[c]}bes8 as bes as } >> |
        << { <as des f as>2->\arpeggio~<as as'>~ \bar"||"
             \key e \major <gis gis'>2 s } \\ 
           { s1 fis,8\p e fis gis gis b,4 gis'8} >> |
        \grace{fis16[gis]} fis8[ e <fis dis><gis e>]
                                 << { b4. cis8 } \\ { <cis,e>4<dis fis> } >> }
      }
      \new Staff {
        \clef bass
        \relative c' {
          \key des \major <as, as,>1| <des f as des>2\arpeggio r|
          \key e \major e,4 b' gis'2| e,4 b' gis'2|
        }
      }
    >>
 }
  
(No points for guessing what this was excerpted from.)

The a flats should resonate into the next bar, which is in E
major, so they have to be tied to g sharps; but apparently the tie
engraver fails to see that they are the same note. What do I have to
\override to overrule it? (I could use a slur but that would create
only one tie and not two.)


-- 
Kilian Foth                                    Phone +49 40 42883-2518
AB NATS, FB Informatik                         Fax   +49 40 42883-2515
Universität Hamburg
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