madrid catalan pro-independence party esquerra republicana de catalunya erc take part snap regional election dec. 21 say monday tactic admission previous rule party catalonia fire parliament dissolve take part dec. 21 opportunity good consolidate republic ... call illegitimate elections trap however afraid ballot box lawmaker sergi sabria say conference spain prime minister mariano rajoy sack regional government dissolve parliament call snap election friday catalonia leaders make unilateral declaration independence region leaders vow ignore rajoy rule continue work catalan pro-independence party say take part december 21 election