  We introduce an entanglement-related quantity that we call the binegativity.
Based on numerical evidence, we conjecture that the binegativity is an
entanglement measure for two-qubit states. The binegativity is compared to the
concurrence and negativity, the only known entanglement measures that can be
computed analytically for all two-qubit states. The ordering of entangled
two-qubit mixed states induced by the binegativity is distinct from the
ordering determined by previously known measures, yielding possible new
insights into the structure of entangled two-qubit mixed states.
