How to start a dictionary/encyclopaedia entry? Let's say I want to define solipsism. Should I write:<br/><br/>Solipsism is a theory that...<br/>or<br/>Solipsism is the theory that...<br/><br/>I'm confused about that, because I found different version in different dictionaries.<br/><br/>Also, is 'that' better than 'according to which'?