Most scientific papers refer to almost any *formula* that contains the "=" sign by the word "equation". Consider this case:

Let `value = function(input) (1)`

where `input`

is a *known* input value and `value`

is the result of the `function`

computation. In this situation, there are no effective unknowns (we are guaranteed that no unknowns are hidden in the `function`

expression either).

Most papers (if not all) often refer to expression (1) in sentences like "equation (1) is equivalent to", "referring to equation (1), we see that..".

Some pedantic referees, however, suggest the use of a more proper word (e.g. *formula* (1) instead of equation (1)).

Is there a grammar reference that solves this seemingly insignificant issue?

*Further clarification*

An example of an expression not considered an equation by a referee: *(a+b)^2 = a^2 + 2ab + b^2 (1)*.

## 1 Answer

I'd say your referee is right.

When you have variables on both sides of an equality, i.e. when you show some relationship between variables, we tend to say this is a formula.

E.g. x + 2y = 3z is a formula.

If, however, one of the sides of your equality contains no variables, just value(s), then we say it's an equation.

E.g. x + 2y = 3 is an equation.

**Edit:** The "equation" environment in LaTeX can be quite confusing this way, as it is often used for formulas, rather than equations...