(S (S (PP (IN In) (NP (BASENP (NN accordance)) (PP (IN with) (NP (BASENP (DT the) (NN Treaty)) (PP (IN on) (BASENP (JJ Open) (NNS Skies))))))) (COMMA ,) (S (BASENP (NNP Norway) (CC and) (NNP Denmark)) (VP (VP (VBD started) (S (VP (VBG conducting) (NP (BASENP (NN observation) (NNS flights)) (PP (IN over) (BASENP (NNP Belarus) (CC and) (NNP Russia))))))) (BASENP (PRP yesterday))))) (PERIOD .))