docs: def _mergeProteinEntries(proteinLists, protToPeps):
      """Returns a new "protToPeps" dictionary with entries merged that are
      present in proteinLists.
  
      NOTE:
          The key of the merged entry is a tuple of the sorted protein keys. This
          behaviour might change in the future; the tuple might be replaced by
          simply one of the protein entries which is then representative for all.
  
      :param proteinLists: a list of protein groups that will be merged
          [{protein, ...}, ...]
      :param protToPeps: dict, for each protein (=key) contains a set of
          associated peptides (=value). For Example {protein: {peptide, ...}, ...}
      :returns: dict, {protein: set([peptid, ...])}
      """
      mergedProtToPeps = dict(protToPeps)
      for proteins in proteinLists:
          for protein in proteins:
              peptides = mergedProtToPeps.pop(protein)
          mergedProtein = tuple(sorted(proteins))
          mergedProtToPeps[mergedProtein] = peptides
      return mergedProtToPeps