Not Really Cryptic Math

[Otis]

Combining sum in a kind of string (6)

 

[Romsek]

series?

 

[firemath]

Knot theory?

Just kidding.

 

[Otis]

series?

Nope.

?

 

[Otis]

Knot theory?

That's sounds about right, firemath. It's not theory.

 

[Romsek]

adding ?

 

[Otis]

adding?

Correct guess.

Spoiler: Answer

Combining = direct
sum = ADD
in = IN
a kind of string = G

Answer = ADDING

 

[Romsek]

Correct guess.

It's a funny thing about the cryptics I do in the papers.
Usually I'll know the answer before I know why it's the answer.
I have to then go figure out why it matches the clue.
Sometimes I never do.

 

[Otis]

… cryptics I do in the papers. Usually I'll know the answer before I know why … Sometimes I never do.

That happened to me, once. Heh. But, I hear you. In the papers, the challenge is to complete the grid, yes? If a guess fits the grid, that's confirmation enough.

I think I'm better at setting than solving, Romsek (and I'm not great at setting). Sometimes, I don't understand answers, even when I have them.

?