be called only once here
</span><span style=color:#72ab00;>>>> </span><span style=color:#b3933a;>2 </span><span style=color:#72ab00;>< </span><span style=color:#5597d6;>factorial</span><span>(</span><span style=color:#b3933a;>3</span><span>) </span><span style=color:#72ab00;>< </span><span style=color:#b3933a;>10
</span><span style=color:#b3933a;>True
</span><span>
</span><span style=color:#7f8989;># another example
</span><span style=color:#72ab00;>>>> </span><span style=color:#d07711;>'bat' </span><span s