Recursion

     (expression) The calling of a procedure by a statement in that same
     procedure.  When a procedure calls itself it is said to recurse.  A
     recursive call causes a new activation of the procedure.  If the source
     code for the procedure includes a declaration of local variables, a new
     set of local variables is created for each activation.  A private
     variable created by the procedure is associated with the activation in
     which it is created, and is visible in that activation and any lower-
     level activations, unless obscured by a private variable created in a
     lower-level activation.