DragginMath: Double-Tap to Replace

When you create a Named Expression, you associate a single-letter uppercase name with an expression. As a convenience, that expression is also loosely associated with the corresponding lowercase variable name.

For example, enter 3≕X. This uses the assign ≕ character, not =. Now whenever you enter X in another expression, its name will be replaced by its value 3.

Also, once you have defined X this way, whenever you use x as a variable in an expression, you will see that its node has a thicker border. Double-tap any thick-bordered variable node to replace its name with its value. Values do not have to be simple operands like numbers: they can be arbitrary expressions.

This value replacement does not happen when you double-tap to evaluate an operator over the variable. You must explicitly ask for it each time for each variable.