<ul>
<li>Start from the boomerang solution shape RRURDLDU,
<li>Place it with the missing corner at up-right position
    and the lower-left tile of "backslash" type (turn image upside-down).
<li>Turn down 180 degrees the upper row of two tiles (valley fold)
<li>Turn left 180 degrees the right column of two tiles (valley fold).
<li>We obtain a 2x2 square with three stacked tiles in the upper-right position and two
    pair of two stacked tile in the two adjacent positions.
<li>Switch the hinging side of these two piles of two stacked tiles and open carefully
    into the final shape
</ul>