olors inverted.</p>

<h4>Note</h4>

<p>If the problems are stored with comments quoting the position
(&quot;Kill upper right corner&quot;) or the color (&quot;Black
to kill&quot;), these modes should not be selected.</p>

<hr size="1" color="#C0C0C0">

<h3>Ratio of previous failures</h3>

<p>Aiming at working more on the more difficult problems, it is
possible to select the ratio of problems previously not solved
with success. A problem is not successfully if it has required
some help (hint, free mode or mo