d(e;e') == if time(e)time(e') time(e')-time(e) else time(e)-time(e') fi 

latex

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clarification:

w-d(w;e;e')
== if w-time(w; e)w-time(w; e') w-time(w; e')-w-time(w; e)
== else w-time(w; e)-w-time(w; e') fi 

latex

Definitions	if b t else f fi, ij, time(e)
FDL editor aliases	w-d