4 ?- trace,derives(impl_i(disj_i1(start(0))), [], impl(atomic(p), disj(atomic(p), atomic(q)))).
   Call: (9) derives(impl_i(disj_i1(start(0))), [], impl(atomic(p), disj(atomic(p), atomic(q)))) ? creep
   Call: (10) derives(disj_i1(start(0)), [atomic(p)], disj(atomic(p), atomic(q))) ? creep
   Call: (11) derives(start(0), [atomic(p)], atomic(p)) ? creep
   Call: (12) lists:nth0(0, [atomic(p)], atomic(p)) ? creep
   Exit: (12) lists:nth0(0, [atomic(p)], atomic(p)) ? creep
   Exit: (11) derives(start(0), [atomic(p)], atomic(p)) ? creep
   Exit: (10) derives(disj_i1(start(0)), [atomic(p)], disj(atomic(p), atomic(q))) ? creep
   Exit: (9) derives(impl_i(disj_i1(start(0))), [], impl(atomic(p), disj(atomic(p), atomic(q)))) ? creep