- "Expression != Expression" -- see Expression -- the class of all expressions
- "Expression != Holder" -- see Expression -- the class of all expressions
- "Expression != Thing" -- see Expression -- the class of all expressions
- "Holder != Expression" -- see Expression -- the class of all expressions
- "Holder != Holder" -- see Expression -- the class of all expressions
- "Thing != Expression" -- see Expression -- the class of all expressions