Soviet constitution which was the basic law of USSR.
First, Crimea turning into an autonomous republic within Ukraine was already contrary to the referendum since restoring the Crimean ASSR would be restoring it as part of RSFSR.
Second, even if we would let my first point slide, Soviet constitution clearly states that an autonomous republic can only exists within an union republic. If Ukraine is no longer a part of the union, this notion doesn't work anymore. This is what has caused the war in Abkhasia in 1992.
Third, here is just one of several examples of using force to keep Crimea on a tight leash through the years. They have tried to become independent several times through the years and were regularly screwed by Ukraine. No wonder they seized the opportunity now.
You fail your history. Have your parents acknowledge your "F" by next week.
Hm, must be a recent and traumatising experience for you, trying to project it on me in such a detail. Let me tell you something, kiddo. I went to schools and universities in several countries. None of these used letters for marks. Have left my parents' basement several decades ago and one day you will grow up and do the same and see the big and very diverse world out there. But until then, get off my lawn.