let sequent_viewer = MatitaMathView.sequentViewer_instance () in
let sequents_viewer = MatitaMathView.sequentsViewer_instance () in
sequent_viewer#set_href_callback
let sequent_viewer = MatitaMathView.sequentViewer_instance () in
let sequents_viewer = MatitaMathView.sequentsViewer_instance () in
sequent_viewer#set_href_callback