S -> NP VP
NP -> DT NN
NP -> NP PP_possession
VP -> VBD NP PP_instrument
VP -> VBD NP
PP_possession -> IN_possession NP  
PP_instrument -> IN_instrument NP
NP -> 'John'
NP -> 'Mary'
DT -> 'a'
DT -> 'the' 
NN -> 'boy' 
NN -> 'man' 
NN -> 'telescope' 
IN_possession -> 'with'  
IN_instrument -> 'with'  
VBD -> 'saw'