&gt; BTW, a long ago in order or incorporate CL into Symbolics Zeta Lisp they used cl: prefix for some functions. Nothing is new under the Moon.)<p>&#x27;cl:&#x27; is no prefix in Zetalisp. Zetalisp uses packages (namespaces for symbols) just like Common Lisp, and &#x27;cl&#x27; is the name of a package and &#x27;:&#x27; is the separator from package name and symbol name. A single colon shows that the symbol is exported - some part of an external interface.<p>Thus cl:let is the &#x27;let&#x27; exported from the &#x27;cl&#x27; package.<p>Emacs Lisp has no packages, no namespaces, no exports, imports, ... So &#x27;cl-&#x27; is a part of the symbol name. It&#x27;s just a prefix.