The problem arises in something we're looking at involving quantum entanglement - each of the a[i][0] + a[i][1] terms (i=0, 1, 2, ..., N-1) represents a two-level quantum state. N such terms multiplied together thus represents a product state of N two-level states. We're then seeing if a general state can be written in this form - if it cannot, then the degree to which it can't is a measure of the degree of entanglement.