LREDUCE

(LREDUCE <function> <list> [<initial>])

The <function> is applied to the first two elements of the <list>, then 
to the result of the previous application and the third element, of the
list, then to the result and the fourth element, and so on. If the <initial>
value s given, the function is first applied to the <initial> and the first
element of the list, then to the result and the second element, etc.

If the <list> is empty, the <initial> value is returned, no calls to
<function> are made. If the <list> is empty and <initial> is not given, the
empty list is returned.

This function equals to the Common Lisp 

   (REDUCE <function> <list> [:initial-value <initial>])

The only exception is that when <initial> isn't given and the <list> is
empty; Common Lisp calls the <function> with no args in this case, while
InteLib Lisp doesn't call it and just returns the empty list.