Pulse Areas in Multi-Soliton Propagation
  The prospect of self-consistent propagation of more than two pulses contemporaneously through multi-resonant media raises open questions: whether soliton solutions exist, and whether a useful generalization of two-level pulse Area can be found. We answer these questions positively for the case of four pulses interacting in combined V and Lambda fashion with an idealized pair of atomic D-lines. 
Elizabeth Groves, B. D. Clader, J. H. Eberly