( We ( ( have ( ( ( ( described ( vertical variations ) ) ( in ( air pressure ) ) ) ( -LRB- ( ( ( air pressure ) ( decreases ( with ( increasing altitude ) ) ) ) -RRB- ) ) ) ( in ( a ( previous lecture ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP have) (VP (VBN described) (NP (JJ vertical) (NNS variations)) (PP (IN in) (NP (NN air) (NN pressure))) (PRN (-LRB- -LRB-) (S (NP (NN air) (NN pressure)) (VP (VBZ decreases) (PP (IN with) (NP (VBG increasing) (NN altitude))))) (-RRB- -RRB-)) (PP (IN in) (NP (DT a) (JJ previous) (NN lecture))))) (. .)))
We have described vertical variations in air pressure (air pressure decreases with increasing altitude) in a previous lecture.
(ROOT (S (NP (NNP Air)) (VP (VBP pressure) (SBAR (S (NP (PRP it)) (VP (VBZ decreases) (PP (IN as) (NP (NN altitude) (NNS increases))))))) (. .)))