s(P1,Number,s(Np,Vp),P3) :-
	np(P1,Number,Np,P2),
	vp(P2,Number,Vp,P3).

np(P1,Number,np(Art,N),P3) :-
	art(P1,Number,Art,P2),n(P2,Number,N,P3).

vp(P1,Number,vp(Verb),P2) :-
	v(P1,Number,Verb,P2).

art(I, Number,art(Word),O) :-
	word(Word,I,O),
	isart(Word,Number).

n(I,Number,n(Word),O) :-
	word(Word,I,O),
	isnoun(Word,Number).

v(I,Number,v(Word),O) :-
	word(Word,I,O),
	isverb(Word,Number).

isart(a,s3).
isart(the,s3).
isart(the,p3).
isnoun(dog,s3).
isnoun(dogs,p3).
isverb(cried,p3).
isverb(cried,s3).


word(the,1,2).
word(dog,2,3).
word(cried,3,4).