(Stamp prices) may increase by a penny.Logical formLearned from21 sentences. A stamp may pertain-to authority.Logical formLearned from21 sentences. Sheets may pertain-to stamps.Logical formLearned from20 sentences. Stamps may pertain-to a language.Logical formLearned from20 sentences. Some stamps can be in a series.Logical formLearned from20 sentences. Stamps may be printed.Logical formLearned from20 sentences. Stamps may pertain-to a nation.Logical formLearned from20 sentences. Sales may pertain-to a stamp.Logical formLearned from20 sentences. A (stamp set) may pertain-to a month.Logical formLearned from20 sentences. A stamp can be valid.Logical formLearned from20 sentences. Some stamps may be used.Logical formLearned from20 sentences. Stamps may arrive.Logical formLearned from20 sentences. A (signature stamp) may pertain-to a person.Logical formLearned from20 sentences. A person may use some stamps.Logical formLearned from20 sentences. A stamp can be annual.Logical formLearned from20 sentences.