Carte Blanche with a Twist by Mash
The initial infinitely repeating grid could be seen alternatively as the surface of a torus,
with opposite edges considered to join up.
The final grid similarly represents the surface of a Klein bottle,
where the top and bottom edges are joined up in reverse.
The grid is supposed to be transparent,
with the entries from the bottom half of the first grid (shown in blue here)
written on the “back” and therefore visible in reverse.
Letters from the back either show through the initial gaps
or are symmetrical and coincide with the letters from the front,
except for an S in the bottom row, which is combined with its reverse
to form an 8 in the eighth column of the submission grid.
Reading the eighth non-space character of each clue spells out “fundamental polygon”,
a term for a diagram such as the final grid that represents a continuous surface,
and “4th dimension”, without which it is not possible to construct a non-intersecting Klein bottle.
The diagonal phrase KLEIN BOTTLE (with the first L and last E reversed) was to be highlighted.