Build the setup.
Understand the loop.

A focused library of published SDPC diagrams, perfect-clear continuations and DPC coverage. Explore the actual solves and the limits of each coverage claim.

How the loop fits together

Five seven-piece bags contain 35 tetrominoes: 140 cells, or 14 complete rows. A successful loop ends on an empty board at the next bag boundary. HOLD and the saved piece are part of that accounting.

SDPC clears eight lines using 20 placed pieces, leaving the 21st piece for DPC. DPC uses that saved piece plus the following two bags: 15 pieces clear six more lines, typically through a T-spin double followed by a perfect clear. A documented SDPC recovery may place the extra piece first and enter a matching recovery-DPC residue instead.

The other common entry is a four-line first PC followed by a four-line second PC. Together they use 20 pieces and reach the same one-piece-leftover boundary. An empty board alone does not establish the correct bag position: track actual pieces consumed and HOLD.