make ties between notes from different voices

[Frédéric Chiasson]

Hi!

I'd like to know how to put ties between a chord from a single voice separating to the same notes but in two differents voice contexts in polyphony.

With this example, the ties does not appear, without any warning though.

Frédéric

P.S. I also tried <a c fis>4~, but the ties still don't appear.

______________

\version "2.11.9"

\relative c''
{ 
    \time 3/4
    r2 <a~ c~ fis~>4
    <<
    {fis'4 e fis} \\
    {<a, c>2.}
    >>
}