Something like 'f(x) = y + 3' can make perfect sense, depending on context.
For example, that could describe a constant function that doesn't depend on x, and y is a free variable that gets its value from context.
Or y could implicitly be a function of x. That happens a lot in calculus or physics.
f = y+3 makes sense f(x) = y+3 does not make sense (at least to me), f(y) = y+3 makes sense however.
f(x) is a function of x correct? It's articulated as "f of x".
> I wonder why you used ':=' instead of '=' to define 'f'. There is no computation going on, right?
:= is assignment in Pascal iirc, maybe that's where it's coming from.