Propositional Logic sentences only. When entering expressions, use Ascii characters only. Use ~ for ¬; use & for ∧; use | for ∨; use => for ⇒; use <=> for ⇔. To avoid ambiguities when entering multiple sentences, terminate each sentence with a period. For example, write "p=>q. p|q." to enter the sentences "p=>q" and "p|q".