before(e) == if first(e) nil else before(pred(e)) @ [pred(e)] fi  (recursive) 

latex

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clarification:

es-before(es; e)
== if es-first(es; e) nil else es-before(es; es-pred(es; e)) @ (es-pred(es; e).nil) fi
(recursive) 

latex

Definitions	pred(e), as @ bs, first(e), if b t else f fi, Y
FDL editor aliases	es-before