;;
;; The dog that barked disappeared.
;;

the:
<_, x0, _>
{ SPEC:<h3, x0, _> }
{ h1:_the_q(x0, h2, _) }
{ h2 =q h3 }
{ }

dog:
<h0, x1, _>
{ }
{ h0:_dog_n_1(x1) }
{ }
{ }

barked:
<h4, e1, x2>
{ SUBJ:<h4, x2, _> }
{ h4:_bark_v_1(e1, x2) }
{ }
{ }

subject extraction LR (barked):
<h4, e1, x2>
{ SLASH: [ <h4, x2, _> ] }
{ h4:_bark_v_1(e1, x2) }
{ }
{ }

[implementation of that LR in terms of an empty argument]

<h4, x2, _>
{ SLASH: [ <h4, x2, _> ] }
{}
{}
{}

that:
<h5, x3, _>
{ MOD:<h5, x3, _> }
{ }
{ }
{ }

that barked:
<h4, e1, x2>
{ MOD:<h5, x3, _> }
{ h4:_bark_v_1(e1, x2) }
{ }
{ h4 = h5 x2 = x3 }