Update sec_antider.ptx

[APEXCalculus]

Possible correction to antidiff. property.

Theorem 5.1.6 states \int c \cdot f(x) , dx = c \cdot \int f(x) , dx.
While this is identical to language in other texts, I got a suggestion that we should add "(c \neq 0)" as a condition.

The reason (which you can figure on your own) is that if c=0, integrating 0 leads to a +C, whereas integrating first then multiplying by 0 means you just get 0.

I'm wondering what others think of this suggestion. I'm lean toward making the change.
Yes, I think they have a point.
I also think the expression "c \cdot \int f(x),dx" is also playing a bit loose with set notation, and this may be an unimportant nitpick. But if it gets students thinking about what's going on, it may create a bit of a learning moment.

Interested in any discussion before someone merges.

[sean-fitzpatrick]

I'm fine with this change. Since we define the indefinite integral as a set, the notation is a little awkward, but in practice I think everyone thinks of the indefinite integral as a representative of this set, with the value of C left unspoken.

Probably the best option (mathematically, not pedagocially) is to think of this set as an equivalence class: we have many examples throughout mathematics of operations on equivalence classes.

[sean-fitzpatrick]

@APEXCalculus I got busy and forgot about this. I think you can go ahead and merge unless further discussion is needed.