Competitive bidding
Transfer Walsh gives us a support double for free: opener completes the transfer with 3-card support even when RHO does not compete. I generalize it to all non-jump responses to end the debate between standard and negative free bids.
We somehow ignore the meaning of overcalls to deal with artificial and psychic bids. If we need to keep the bidding open, the nebulous 1♠ gets the job done.
This competitive Transfer Walsh is the Cachalot (O. Bessis, Le Bridgeur 852, 2011; Soulet–Voldoire, 909, 2017), which I also play over the Polish Club. Unlike the uncontested transfers, the free bids are constructive, 6+, so opener need not keep a broke responder low. The 1M completion promises exactly 3-card support, 11–17, like a support double. A balanced minimum with a doubleton no longer completes.
Over 1♦, the Cachalot applies to the one-level overcalls in the majors.