title: From SQL to tuple relational calculus with Join
body: <p>I have two SQL-queries I need to convert into tuple relational calculus. The first query</p>
  
  <pre><code>SELECT immobilie.*
  FROM immobilie
  WHERE 'Preis'&lt;'100000'
  </code></pre>
  
  <p>seems to be pretty obvious (if I understood it right):</p>
  
  <pre><code>{w|w ϵ MAKLER ∧ w.Preis &lt; `100000‘} 
  </code></pre>
  
  <p>But the second one:</p>
  
  <pre><code>SELECT makler.*
  FROM makler
  JOIN immobilie
       ON makler.MaklerID = immobilie.angebotenVon
  WHERE immobilie.Typ = 'Wohnung'
  </code></pre>
  
  <p>has a join and I couldn't find a good example how I would need to convert it. Could anyone help me with an explanation?</p>