# Is it correct to use a comma in this equation?

Consider:

Then, the sequence $k_i$ given by (3.38) is increasing and converges to
$$\label{eq:weired_equation} k^\xi = k_1\times k_2 \times c \times d,$$
where $c$ and $d$ are defined in the Theorem 2.


I have the questions:

1. What are the grammatical errors in the above piece?
2. Should a comma be used after the equation \eqref{eq:weired_eqution}.
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@WillHunting I don't 100% agree with you, mathematical language has some specifics, and mathematical typography as well. IMHO, this question is boundary here, but still ok. –  tohecz Nov 25 '12 at 19:45
I'm 100% sure that the comma is correct (see my answer). On the other hand, I think that (1) There should be no comma after Then, and (2) there should be no the before Theorem 2 (you write Theorem with capital T, hence it is like a name). However, I'm not a native speaker, and one such should confirm what I say. –  tohecz Nov 25 '12 at 19:48
@tohecz: math.stackexchange.com exists :-) –  Martin Schröder Nov 26 '12 at 9:50

There should be no difference in punctuation whether you write the equation on display or inside the text.

So since there would be a comma if written inside the text, the comma is correct.

Considering the 1st question, see my comment. In the end, the piece can look like

Then the sequence $k_i$ given by (3.38) is increasing and converges to
$$\label{eq:weired_equation} k^\xi = k_1\times k_2 \times c \times d,$$
where $c$ and $d$ are defined in Theorem 2.


In the label, there's a typo and it should be weird_equation, but I did not correct this to avoid you problems with cross-referencing.

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