@prefix e: <http://eulersharp.sourceforge.net/2003/03swap/log-rules#>.
@prefix : <http://eulersharp.sourceforge.net/2007/07test/id#>.

:a :r :b.
:b :r :c.
:c :r :d.

({?X :r ?Y} {?X :t ?Z. ?Z :t ?Y})!e:disjunction => {?X :t ?Y}.
{?X :t ?Y} => ({?X :r ?Y} {?X :t ?Z. ?Z :t ?Y})!e:disjunction.

:f :t :a.
{:f :r ?X} => false.

{{?X :t ?Y} => ({?X :r ?Y} {?X :t ?Z. ?Z :t ?Y})!e:disjunction} e:tactic (() _:G).
