That is to say, beside Indo-European and Indo-Hittite, there must have existed an Indo-Slurvian.
( ( That ( is ( to ( ( say , ) ( beside ( ( Indo-European and ) Indo-Hittite ) ) ) ) ) ) ( , ( there ( ( must ( have ( existed ( an Indo-Slurvian ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (DT That)) (VP (VBZ is) (S (VP (TO to) (VP (VB say) (, ,) (PP (IN beside) (NP (NNP Indo-European) (CC and) (NNP Indo-Hittite)))))))) (, ,) (NP (EX there)) (VP (MD must) (VP (VB have) (VP (VBN existed) (NP (DT an) (NN Indo-Slurvian))))) (. .)))
There must definitely not exist an Indo-Slurvian.
( There ( ( ( ( must definitely ) not ) ( exist ( an Indo-Slurvian ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (MD must) (ADVP (RB definitely)) (RB not) (VP (VB exist) (NP (DT an) (NN Indo-Slurvian)))) (. .)))