Messiaen had also been composing a concerto for four musicians he felt particularly grateful to : his wife Loriod , the cellist Mstislav Rostropovich , the oboist Heinz Holliger and the flautist Catherine Cantin .
On going through his papers , Messiaen 's widow discovered that he had been composing a concerto for four musicians he felt particularly grateful to , namely Loriod , the cellist Mstislav Rostropovich , the oboist Heinz Holliger and the flautist Catherine Cantin ( hence the title Concert Ã quatre ) .