 the final expression to return</li>
<li>an assignment starts a statement, it is not an operator</li>
<li>single character variables are reserved.  Assignments to reserved built-ins throw an exception;  e.g. <samp>r=3.0; r</samp> returns <em>Attempted assignment to non-UserSymbol 'r' at '3.0'</em>.</li>
<li>unary operators have a lower priority than binary operators, that is, the unary minus (negation) has lower precedence than exponentiation, so -3^2 is interpreted as -(3^2) = -9.  Use parentheses to clari