private List<HornClause> asHornClauses(List<Sentence> sentences)
{
List<HornClause> hornClauses = new List<HornClause>();
for (int i = 0; i < sentences.Count; i++)
{
Sentence sentence = (Sentence)sentences[i];
HornClause clause = new HornClause(sentence,this);
hornClauses.Add(clause);
}
return hornClauses;
}