Part 1 - The photochemistry of 1,3,4,5,6,6-hexamethylbicycio[3.1.0]hex-3-en-one. Part II - The acid-catalyzed rearrangements of 1,3,4,5,6,6-hexamethylbicyclo[e.1.0]hex-3-en-2-one and 2,3,4,5,6,6-hexamethyl-2,4-cyclohexadienone