Terminal Context in Context-Sensitive Grammars

If every non-context-free rewriting rule of a context-sensitive (with erasing) grammar has as left context a string of terminal symbols and the left context is at least as long as the right context, then the language generated is context-free. If every non-context-free rewriting rule of a context-sensitive (with erasing) grammar has as left and right context strings of terminal symbols, then the language generated is context-free.