Apparently neither the Lib Dems nor Plaid will be standing in Vale of Glamorgan, which is Alun Cairn's seat

Between them they won 3,315 votes in 2017 (2,295 for Plaid and 1,020 for Lib Dems), this would be enough votes for to push Labour over the line and unseat Cairns, in fact just the 2,295 votes Plaid received would be enough. The Greens won only 419 votes last time and the assumption that LD and PC voters will just back them when they have a chance to unseat a Tory is bizarre

This has almost definitely been calculated to unseat Cairns, which will give Labour the seat