question: By what year had the situation in Europe cool down enough so that Joao VI would have been able to safely return to Lisbon ?
answer: 1815
turker_answer: By 1815 the situation in Europe cooled down enough so that Joao VI would have been able to safely return to Lisbon .
rule-based: Had the situation in Europe cool down enough so that Joao VI would have been able to safely return to Lisbon by 1815 .