help on note head, thanks

[Jinsong Zhao]

Hi there,

In a violin score, I saw something similar to the following code, but 
the second voice b4 was displayed as a triangle. I can not recognize it, 
and don't know how to input it into lilypond. Any help? Thanks in advance.

\relative c' {
  \key g \major
  << {dis16 [fis b, ais]} \\  {s \omit Stem b4} >>
}

Best,
Jinsong