Document behaviour of -1² in Traps

Closes #971

doc/Language/traps.pod6

@@ -334,6 +334,21 @@ statements in other languages like C<return>, C<last> and many others.
     }
     say f; # OUTPUT«True␤»
 
+=head2 Exponentiation Operator and Prefix Minus
+
+    say -1²;   # -1
+    say -1**2; # -1
+
+When performing a
+L<regular mathematical calculation|http://www.wolframalpha.com/input/?i=-1%C2%B2>,
+the power takes precedence over the minus; so C<-1²> can be written as C<-(1²)>.
+Perl 6 matches these rules of mathematics and the precedence of C<**> operator is
+tighter than that of the prefix C<->. If you wish to raise a negative number
+to a power, use parentheses:
+
+    say (-1)²;   # -1
+    say (-1)**2; # -1
+
 =head1 Subroutine and method calls
 
 Subroutine and method calls can be made using one of two forms: