mod131.hs:2:27:
    Conflicting exports for ‘f’:
       ‘module Mod131_B’ exports ‘f’
         imported from ‘Mod131_B’ at mod131.hs:3:17
         (and originally defined at Mod131_B.hs:3:1)
       ‘Mod131_A.f’ exports ‘Mod131_A.f’
         imported qualified from ‘Mod131_A’ at mod131.hs:4:27
         (and originally defined at Mod131_A.hs:3:1)