Complex sentence: A dome is a self-supporting structural element of architecture that resembles the hollow upper half of a sphere; this definition excludes structures such as The O 2 (formerly the Millennium Dome) in London which is in diameter and supported by masts.
Split into simpler sentences: A dome is a self-supporting structural element of architecture that resembles the hollow upper half of a sphere. This list excludes dome-shaped structures that are not self-supporting such as The O 2 (formerly the Millennium Dome) in London which is in diameter and supported by masts.