title: How to add legend manually without overwriting the others legends in ggplot2
body: <p>First, below is my code</p>
  <pre><code>library(ggplot2)
  
  x1 &lt;- rnorm(200)
  x2 &lt;- rnorm(200,2,1) 
  
  y &lt;- ifelse(1 + 3*x1 - x2 &gt; 0, &quot;1 + 3*x1 - x2 &gt; 0&quot;, &quot;1 + 3*x1 - x2 &lt; 0&quot;)
  z &lt;- ifelse(-2 + x1 + 2*x2 &gt; 0, &quot;-2 + x1 + 2*x2 &gt; 0&quot;, &quot;-2 + x1 + 2*x2 &lt; 0&quot;)
  dat &lt;- data.frame(x1,x2,y,z)
  ggplot(data = dat) + geom_point(aes(x1,x2, col = y, shape = z)) + 
  geom_abline(intercept = 1, slope = 3, color=&quot;red&quot;, size=1.5) +  
  geom_abline(intercept = 1, slope = -0.5, col = &quot;green&quot;, size = 1.5)
  </code></pre>
  <p><img src="https://i.stack.imgur.com/eI308.png" alt="enter image description here" /></p>
  <p><strong>I want to add another legend</strong> with:</p>
  <ul>
  <li>title = &quot;Hyperplanes&quot;</li>
  <li>red solid line = &quot;1 + 3*x1 - x2 = 0&quot;</li>
  <li>green solid line = &quot;-2 + x1 + 2*x2 = 0&quot;</li>
  <li>position = bottom of the plot</li>
  </ul>
  <p>Can you help me?</p>