Complex sentence: In 1990, Nikos Alexiou proposed a collaboration, using his own work as a base for Dimitris Papaioannou to work upon, so they created "The Last Song of Richard Strauss", which later became "The Songs" trilogy.
Split into simpler sentences: In 1990, Nikos Alexiou proposed a collaboration, using his own work as a base for Dimitris Papaioannou to work upon. They created "The Last Song of Richard Strauss", which later became "The Songs" trilogy.