Round Robin explained

A round robin bets every combination of a chosen size across your selections — commonly all doubles from four, five or six picks. Trixie and Yankee are just branded round robins of fixed sizes; the general form lets you choose the width.

The combinatorics grow fast: all doubles from six picks is fifteen bets, all trebles twenty. Each combination carries its own stake and its own margin, so the structure multiplies the bookmaker's cut exactly as fast as it multiplies your coverage.