w-pred(w;e)
== if (time(e) = 0)
== ifthen inr  
== if isnull(a(loc(e);time(e) - 1))
== ifthen w-pred(w;<loc(e), time(e) - 1>)
== else inl <loc(e), time(e) - 1> 
== fi 

---

clarification:

w-pred(w;e)
== if (w-time(w; e) = 0)
== ifthen inr  
== if w-isnull(w; w-a(w; w-loc(w; e); (w-time(w; e) - 1)))
== ifthen w-pred(w;<w-loc(w; e), w-time(w; e) - 1>)
== else inl <w-loc(w; e), w-time(w; e) - 1> 
== fi 
(recursive) 

latex

Definitions	Y, x.A(x), (i = j), inr x , , if b then t else f fi , isnull(a), a(i;t), f(a), inl x , <a, b>, loc(e), n - m, time(e), #$n
FDL editor aliases	w-pred