S -> SN SV
	SP -> P SN
	SN -> Det N | SN SP
	SV -> V SN | SV SP
	Det -> "el" | "la" | "un" | "una" | "los" | "las"
	N -> "tren" | "telescopio" | "noticia" | "mesa" | "hombre" | "casa" | "amiga"
	V -> "vio" | "leí" | "encontró"
	P -> "en" | "sobre" | "con" | "de" | "a"