Complex sentence: For a time after the fourth night, Robert cannot find the Number Devil in his dreams; later, however, on the fifth night, Robert finds himself at a desert where the Number Devil teaches him about triangular numbers through the use of coconuts.
Split into simpler sentences: For a time after the fourth night, Robert cannot find the Number Devil in his dreams. Later, however, on the fifth night, Robert finds himself at a desert where the Number Devil teaches him about triangular numbers through the use of coconuts.