overlaying noteheads in different voices

[Charles O. Lawrence]

How do I get the dotted half low a in voice 2 to overlay (blot out? I don’t know the proper terminology) the eighth low a in voice 1?

 

I searched the LSR, but came up empty, probably because I don’t know the proper lilypond terminology for this notation.

 

\new Staff

    \relative c'' {

    \time 6/8

    <<

      \new Voice = "1" { \voiceOne {a,8 a' b c d e | }}

      \new Voice = "2" { \voiceTwo {a,,2. }}

    >>

    \bar "|." }

 

Thanks,

Charles