  Recently, we introduced negativity fonts as the basic units of multipartite
entanglement in pure states. We show that the relation between global
negativity of partial transpose of N- qubit state and linear entropy of reduced
single qubit state yields an expression for global negativity in terms of
determinants of negativity fonts. Transformation equations for determinants of
negativity fonts under local unitaries (LU's) are useful to construct LU
invariants such as degree four and degree six invariants for four qubit states.
The difference of squared negativity and N-tangle is an N qubit invariant which
contains information on entanglement of the state caused by quantum coherences
that are not annihilated by removing a single qubit. Four qubit invariants that
detect the entanglement of specific parts in a four qubit state are expressed
in terms of three qubit subsystem invariants. Numerical values of invariants
bring out distinct features of several four qubit states which have been
proposed to be the maximally entangled four qubit states.
