> not a function, but a value calculated from some other values The term of art is "an expression" [0]. And you can also differentiate expressions with respec

> not a function, but a value calculated from some other values The term of art is "an expression" [0]. And you can also differentiate expressions with respect to their variables. It's a perfectly supported construction in all symbolic computer algebra packages. No need to assign an (arbitrary) ordering to your variables in order to differentiate with respect to them. [0] https://en.wikipedia.org/wiki/Expression_(mathematics) https://en.wikipedia.org/wiki/Expression_(mathematics)