incidenceCorrespondence L
i1 : I = incidenceCorrespondence({1,2,3}) o1 = I o1 : an incidence correspondence from a flag bundle to a flag bundle
i2 : source I o2 = a flag bundle o2 : a flag bundle with subquotient ranks {1..2}
i3 : target I o3 = a flag bundle o3 : a flag bundle with subquotient ranks {2, 1}