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
                                              (defined at Mod164_A.hs:3:10)
                          or `Mod164_B.D1', imported from Mod164_B at mod164.hs:5:1-15
                                              (defined at Mod164_B.hs:3:10)