Undefined commands in langsci-textipa

[kopeckyf]

When langsci-textipa.sty is loaded in a minimal langscibook document, these commands are reported as undefined:

l.48 \renewcommand{\textepsilon}
                                {ɛ}
l.55 \renewcommand{\textgamma}
                              {ɣ}
l.115 \renewcommand{\textrho}
                             {ρ}
l.155 \renewcommand{\textsigma}
                               {}

This also happens in some live book projects. It looks a bit odd that \textsigma has an empty definition.