An action can be hollow.Logical formLearned from4 sentences. A guarantee can be hollow.Logical formLearned from4 sentences. A campaign can be hollow.Logical formLearned from4 sentences. A tune can be hollow.Logical formLearned from4 sentences. Protestations may ring hollow.Logical formLearned from4 sentences. Minds can be hollow.Logical formLearned from4 sentences. (Support columns) can be hollow.Logical formLearned from4 sentences. A base can be hollow.Logical formLearned from4 sentences. Bristles can be hollow.Logical formLearned from4 sentences. A bluster can be hollow.Logical formLearned from4 sentences. A requirement can be hollow.Logical formLearned from4 sentences. A face can be hollow.Logical formLearned from4 sentences. Ice can be hollow.Logical formLearned from4 sentences. (Iron pillars) can be hollow.Logical formLearned from4 sentences. A position may sound hollow.Logical formLearned from4 sentences.