[sty2000]

Over natural 1♣ opening (2+ cards), we play Walsh, so 1♦ bid denies 4M unless responder has at least invitational hand. Also, after 1NT rebid by opener, we play Two-way checkback: 2♣ is transfer to 2♦ which responder passes with weak hand and diamonds or bids on with invitational hand, and 2♦ is game forcing relay.

Suppose you have two sequences like this:

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How do you treat partner's Dbl in above sequences? Is it a "stolen bid" double, or negative double or something else?

[whereagles]

You can play it as penalties because if responder has a major, he can bid it now.

[Zelandakh]

Don't you want to know what 2♦ means before deciding on the meaning of double? It is surely not natural here - I would think it shows the majors for most, which might in turn affect the meaning you assign to Responder's 2M rebids.

[helene_t]

It is certainly not stolen bid.

The first one I would take as penalty although it could be offering opener the option to take it out with three diamonds and less than four clubs.

The second one, assuming that the 2♦ overcall shows both majors, could be played either as showing diamonds or showing interest in defending 2M doubled. Probably you play it as penalty-oriented in similar situation when opps make a Michael's cuebid and then you might find it easier to play it here also.

[mgoetze]

Rule 1: Double is never stolen bid except for Stayman double of 1NT-(2♣)
Rule 2: Double is for takeout unless it doesn't make sense.
Rule 3: If it doesn't make sense, then double is for penalty.

Simple application of these 3 basic rules leads to the obvious conclusion that these are penalty doubles.