How many movies have Hisao Ohkawa and Isao Takahata collaborated on?

They have worked on 4 movies together! Their first movie together was Heidi in the City (1977) while their highest rated movie together was Heidi, Girl of the Alps (1979). They have not worked together since Alps no Shōjo Heidi: Heidi to Clara Hen (1993). They are most known for their animation films together.