Read the original tetx at El Pais.
You want to believe that there are no precedents? Of course, there are precedents. They were created when the fait accompli prevailed over the rule of law. The law on the transitional period, which establishes a separate (albeit temporary) Constitution, adopted even before it is submitted to a referendum, can be considered a completed fact.
The same thing happened in Crimea; the difference is that foreign troops – Russian army – have entered the peninsula. With the exception of this, everything else happened spontaneously, unilaterally and illegally.
Historical belonging of Crimea has always been disputable. A referendum on separation was unilaterally on May 25, 2014. When February came, the Supreme Council of Crimea rescheduled it to March 30. March 6, the terms were postponed again (to March 16). Russian troops were already on the peninsula, Crimean authorities declared independence on March 11, and voting in a referendum took place five days later, on March 16. And in some 48 hours Russia has annexed the peninsula.
March 21, the Council of Europe declared that it did not recognize the results of the vote, since it was "a violation of the Constitution of Ukraine." March 24, a similar statement was made by the UN General Assembly. Thus, Russian Crimea became an outcast region, recognized only by Moscow and Minsk.
The completed facts were in clear contradiction with the legal status and the Basic Law. "The sovereignty of Ukraine extends over its entire territory," Article 2 of its Constitution says. Then it says that Ukraine is a "unitary state" with "inviolable" borders. Moreover, "the issues of territorial changes are decided solely on the all-Ukrainian referendum."
March 21, the Venice Commission of the Council of Europe (Russia is one of its members), said that the accession was illegal. It stressed that ten days were too short a period. Any referendum must be preceded by serious negotiations between the players. Venice Commission has also noted that a preliminary statement of separation "aroused doubts" about "impartial position of the authorities of the peninsula."
By the way, the then President of the Generalitat of Catalonia Artur Mas exclaimed indignantly: "Comparing Catalonia and Crimea is madness." Madness? Probably, the authorities of Crimea were lucky that because of the roar of Russian tanks, few people could hear their demagoguery.
Having invaded the peninsula, they violated ten binding international legal regulations (Jean-Dominique Giuliani, Russia, Ukraine and International Law, F. Robert Schuman, doc. 344, 17/2/2015). Catalans are lucky that their neighbor is Andorra, not Putin's Russia.