by Kiran Kedlaya (with help from Ray Jones)
There's nothing hidden here; you simply have to figure out some way to sift
through the 19! possible assignments of characters to operations. There are
a number of ways to do this. One is to generate possibilities for the
first few letters, sort through them to find the most plausible beginning of
the message, then generate all possibilities for the next 10 letters or so
and find the most plausible continuation. At that point, you have cut the
search space down so much that you can just list the possibilities and pick out
the obvious correct one. Another approach is to perform a trimmed branching,
matching words against a word list.
All of the words in the message are in several online dictionaries (including
wamerican on debian). A python script that solves the puzzle in about 15
minutes with a dictionary of 100k words is here. It uses prefix and word
trimming. It took around two hours of work to write.
The correct message reads
FIND THE FAKE WARHOL HOMAGE IN THE STUDENT ART GALLERY
The Wiesner Student Art Gallery is located on the second floor of
W20 (a/k/a Stratton, a/k/a the Student Center). Solvers will therein
find a tastefully presented can of Campbell's Tomato Soup. That can is
the answer to the puzzle.
Postscript: the operations in the order listed correspond to
H, E, W, K, D, T, M, O, G, N, U, L, space, I, R, S, F, A, Y. There is nothing
special about this order per se; it was chosen (using a hill climbing
iteration) to maximize the number of letters that could be fit into the
grid (in this case, 54 out of 81).