mod164.hs:9:5:
    Ambiguous occurrence ‘D1’
    It could refer to either ‘Mod164_A.D1’,
                             imported from ‘Mod164_A’ at mod164.hs:4:1-15
                             (and originally defined at Mod164_A.hs:3:10-11)
                          or ‘Mod164_B.D1’,
                             imported from ‘Mod164_B’ at mod164.hs:5:1-15
                             (and originally defined at Mod164_B.hs:3:10-11)