A bomb went off under my bed the other morning. It was early on a grey Tuesday when heard a flock of ambulances somewhere near my Left Bank Street, making that forlorn, politely insistent two- note bleating all Paris ambulances make. I went downstairs and outside and found nothing. The strcet sweeper with the green plastic broom was sweeping; the young woman who keeps the striped pajama boutique across the street was reading her Paul Auster novel. ("You left New York for Paris?" she demanded incredulously when I introduced myself not long ago.)Only in the early afternoon, when