In geometry, there are surfaces that do without an inside or outside—and some need at least four dimensions to exist ...

Mark Cussen, CMFC, has 13+ years of experience as a writer and provides financial education to military service members and the public. Mark is an expert in investing, economics, and market news.

Julia Kagan is a financial/consumer journalist and former senior editor, personal finance, of Investopedia. Toby Walters is a financial writer, investor, and lifelong learner. He has a passion for ...