Independence characterization for sufficient reducts

Let TWT_W be a theory in a signature LWL_W, with reducts TwT_w to a sufficient collection of subsignatures LwL_w. Assume that MWM_W is a monster model of TWT_W, that TWT_W and every TwT_w are simple (respectively rosy), and that \mathpalette\IndW\mathop{\mathpalette\Ind{}}^W and \mathpalette\Indw\mathop{\mathpalette\Ind{}}^w denote forking (respectively thorn-forking) independence. Let CA,BMWeqC\subset A,B\subset M_W^{eq} be algebraically closed in the sense of TWeqT_W^{eq}.

Independence characterization conjecture. Then

A\mathpalette\IndCWB if and only if A\mathpalette\IndCwB for all w.A \mathop{\mathpalette\Ind{}}^W_C B \text{ if and only if } A \mathop{\mathpalette\Ind{}}^w_C B \text{ for all } w.

The claim seeks to characterize independence in the full theory using independence in all reducts. The source gives related one-way results and notes that the converse is immediate in stable theories, while the general simple or rosy case remains conjectural.

Sources & referencesView supporting material

Primary source

Alice Medvedev, “QACFA”, arXiv:1508.06007 (2015).

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