=IF(C1="",IF(B2="","",IF(D2="",IF(AND(B3="",D3<>""),"┐",""),IF(B3="","┬","─"))),IF(B2="",IF(OR(C1="─",C1="└"),"",IF(D2="","│",IF(B3="","├","└"))),IF(D2="",IF(AND(B3="",D3<>""),"┐",""),IF(AND(B3="",D3<>""),"┬","─"))))