code: @Nonnull
    public EChange removeFunction (@Nonnull final QName aName, @Nonnegative final int nArity)
    {
      final XPathFunctionKey aKey = new XPathFunctionKey (aName, nArity);
      return removeFunction (aKey);
    }
docs: Remove the function with the specified name.
  
  @param aName
  The name to be removed. May not be <code>null</code>.
  @param nArity
  The number of parameters of the function. Must be &ge; 0.
  @return {@link EChange}