( It ( ( ( ( is not ) necessary ) ( that ( ( ( atom-num1 and ) atom-num2 ) ( are ( connected ( by ( a ( covalent bond ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (RB not) (ADJP (JJ necessary)) (SBAR (IN that) (S (NP (JJ atom-num1) (CC and) (NN atom-num2)) (VP (VBP are) (VP (VBN connected) (PP (IN by) (NP (DT a) (JJ covalent) (NN bond)))))))) (. .)))
It is not necessary that atom-num1 and atom-num2 are connected by a covalent bond.
(ROOT (S (NP (DT A) (NN covalent) (NN network)) (ADVP (RB solid)) (VP (VBZ is) (NP (NP (DT a) (NN compound)) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (NP (DT all)) (PP (IN of) (NP (DT the) (NNS atoms)))) (VP (VBP are) (VP (VBN connected) (PP (TO to) (NP (CD one) (DT another))) (PP (IN by) (NP (JJ covalent) (NNS bonds))))))))) (. .)))