The pattern for this common design is often shown without the instructions for making a corner.
I have designed my version of a corner. . . . .
. . . . and the instructions on how to make it.
Uses two shuttles, starting along the straight edge.
R(3-3-3-3), reverse work (RW).
Switch Shuttles (SS), R(3-3-3-3), do not reverse (DNR).
(*) SS, C(4) DNR.
R(3+3-3-3) join to last picot of adjacent ring (first ring made), RW.
SS, R(3+3-3-3), join to last picot of adjacent ring (2nd ring made), DNR.
Repeat from (*) until ready to make the corner, as follows;
After completing the last pair of the facing rings, make C(3), RW.
R(3+3-3-3-3-3) join to the last picot of the adjacent ring, RW.
C(3+), lock join to the inside ring of the the last pair of rings before the turn, RW.
R(3+3-3-3) join to the last picot of the ring in the corner, DNR.
Repeat from (*) until ready to make the next corner.