Fig. 2.

(2a) shows how a hairpin can be inserted in our model, with both extremities stacked, or overlapping a canonical base pair. In (2b) we show the last configuration, where we require the hairpin to be between the components of a 2-way junction and to have at least one extremity stacked. In (2c) we show another view of Figure 1 without the base pairs overlapping the 3-way junction. We can notice that we can go from any component of the 3-way junction to any other without crossing the base pairs