docs: def build_tri(adf):
          """
          Looks at each column, and chooses the feed with the most recent data
          point. Honours the Trump override/failsafe logic. """
          # just look at the capital (price), in "feed one", and income (dividend), in "feed two"
          
          cap, inc = adf.columns[1:3]
          
          data = adf[[cap,inc]]
  
          # find the feeds with the most recent data...
          inc_pct = data[inc].div(data[cap].shift(1))
          
          cap_pct = data[cap].pct_change(1)
          
          pre_final = inc_pct + cap_pct
          
          # create the final, applying the override and failsafe logic...
          final_df = pd.concat([adf.override_feed000,
                                pre_final,
                                adf.failsafe_feed999], axis=1)
          final_df = final_df.apply(_row_wise_priority, axis=1)
          return final_df