Substituted 2,7-dioxo-2,7-dihydrobenzo[1:2-b; 5:6-b.sup.1 ]difuran or -dipyrrole dyestuffs, their preparation and their use

Granted: Jun 8, 1982 Filed: Jul 10, 1980

This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.