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I'm new to forest and trying to figure out some of the finer details. I have a tree where the root node has three children. I would like the root node to be centered above the middle child. Here is the code:

\documentclass{standalone}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[normalem]{ulem}

\usepackage{forest}

\begin{document}

\begin{forest}
[S
   [S
      [DP[John]]
      [VP
         [V[likes]]
         [DP[\sout{opera}]]
      ]
   ]
   [and%, before computing xy={s/.average={s}{siblings}}
   ]
   [S
      [DP[Mary]]
      [VP
         [V[dislikes]]
         [DP[opera]]
      ]
   ]
]
\end{forest}

\end{document}

And here is the result:

enter image description here

calign=center or variations thereon will not work because the three subtrees have different widths. I could manually adjust the s sep, but that is a lot of hassle if I have to do more than one tree. According to the forest documentation (and the answer to this question), I should be able to add , before computing xy={s/.average={s}{siblings}} to the node containing 'and' and get the result I'm looking for. However, when I try this I get the error "Package pgfkeys Error: I do not know the key '/forest/s/.average', to which you passed '{s}{siblings}', and I am going to ignore it. Perhaps you misspelled it."

What's going on here? This is my first question here, so please let me know if you need further information.

closed as off-topic by cfr, TeXnician, Stefan Pinnow, Troy, Schweinebacke Nov 7 '17 at 7:53

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  • What version of Forest do you have? I think you need to update. – cfr Nov 7 '17 at 4:44
  • 4
    I'm voting to close this question as off-topic because the problem is caused by outdated software and can be resolved by updating. (.average does not exist in older versions, but the code works fine with this addition in current Forest.) – cfr Nov 7 '17 at 4:49