diff --git a/symmetry/crossbow/crossbow.mzn b/symmetry/crossbow/crossbow.mzn
index c5fbcf3..fc94a33 100644
--- a/symmetry/crossbow/crossbow.mzn
+++ b/symmetry/crossbow/crossbow.mzn
@@ -1,20 +1,30 @@
+% Arrange 'n' crossbow traps on an 'n' x 'n' discrete grid of squares
+% so that they don't target each other. Find any acceptable solution.
+% (This is exactly the n-queens problem.)
+ 
 int: n;
+ 
 set of int: N = 1..n;
-array[N,N] of var bool: t; 
+array[N,N] of var bool: t;
 constraint sum(i,j in N)(t[i,j]) = n;
 solve satisfy;
-
-% no two traps on the same row
+ 
+% no two traps on the same row (constant i)
 constraint forall(i in N)(sum(j in N)(t[i,j]) <= 1);
-% no two traps on the same column
+ 
+% no two traps on the same column (constant j)
 constraint forall(j in N)(sum(i in N)(t[i,j]) <= 1);
+ 
 % no two traps on same diagonal
+% case of both i and j increasing, so i-j must be a constant k in 1-n..n-1
 constraint forall(k in 1-n..n-1)
       (sum(i,j in N where i-j=k)(t[i,j])<= 1);
+ 
+% no two traps on same diagonal
+% case of i decreasing as j increases, so i+j must be a constant k in 2..2*n
 constraint forall(k in 2..2*n)
       (sum(i,j in N where i+j=k)(t[i,j])<= 1);
-
-
+ 
 output [ if fix(t[i,j]) then "T" else "." endif ++
-         if j = n then "\n" else "" endif 
-       | i,j in N];
\ No newline at end of file
+         if j = n then "\n" else "" endif
+       | i,j in N];