Algebra uses letters and symbols in the place of numbers and can be used to simplify expressions. Algebraic notation close algebraic notationA series or system of written symbols used to represent ...

By "expression" Darwin meant any bodily movement or posture ("body language"), not just facial expressions. He wrote of horses scratching themselves by nibbling those parts they can reach ...

They must know what they have written and where the insertion point is so they can add or delete characters. Understanding longer or more complex expressions requires navigating within the expression ...