to be piled up; to lie on top of one another; piled up; to lie on top of one another; to come one after another; to happen over and over; to pile up ; to accumulate; come one after another; to happen over and over; to pile up ; to accumulate; to overlap ; to occur at the same time; to happen simultaneously; overlap ; to occur at the same time; to happen simultaneously; main; principal; chief; leading; important
