Brexit is causing many problems. The narrow referendum win secured by simple fiction is struggling to cope with complex truth. Unsurprisingly, the problems are thorniest in Ireland. At least since the plantation of Ulster, two conflicting fictions have caused recurring conflict. For Unionists, the fiction that Belfast is as British as Finchley, and for Republicans, that it is as Irish as Dublin. The binary trap of one place and two identities seemed inescapable. But remarkably, after centuries of often bloody stalemate a creative compromise finally promised escape. Prime Minister Margaret Thatcher signed the Anglo-Irish Agreement with Taoiseach Garrett Fitzgerald in…