title: ocamlfind: Package `core' not found
body: <p>I've installed <code>core</code> using <code>opam</code>, added opam config to the bash environment,
  but I can't compile a program using the core module (the module is installed):</p>
  
  <pre><code>$ opam install core
  [NOTE] Package core is already installed (current version is 113.33.03).
  
  $ ocamlfind ocamlopt -o progprog -linkpkg -package core test1.ml
  ocamlfind: Package `core' not found
  </code></pre>
  
  <p>If I do <code>ocamlfind list</code> I can't see the package (<code>core</code>) in the list.</p>
  
  <p>What could be the reason?</p>