/// <summary>
/// Returns the inverse of the specified element.
/// </summary>
/// <param name="element">The element.</param>
/// <returns>The inverse of element (-element)</returns>
/// <exception cref="InvalidCastException">When the cast to DirectSum from interface was not possible</exception>
public DirectSum <T, TGroup> Inverse(DirectSum <T, TGroup> element)
{
var tuple = element.InverseElement() as DirectSum <T, TGroup>;
if (tuple == null)
{
throw new InvalidCastException();
}
return(tuple);
}
