In mathematics, I often see phrases like
“Let f(x) be a function with a critical point at, say, x1.”
In sentences like this an element of a set has a special property and we would like to assign that element a label (such as x1 in the case above), how should the above phrase be punctuated?
My instinct says it should be “at, say, x1” but a google search reveals “at say x1” shows up quite frequently. I suspect that it’s entirely up to writing style but I haven’t been able to find anything that makes me confident about whether I should prefer one or the other.
The construction with two commas looks more natural.
I googled “at, say, x=0”, and saw examples with no commas, one comma and two commas.
The one-comma version looks unbalanced, as others have pointed out. The only no-comma version that looked right was in a very dense paper where almost no punctuation was used in the explanatory text.
It’s difficult to judge the English written by mathematicians and engineers, since the placement of commas in the text is usually not their main concern.
However, a good source of examples in mathematical writing is the documentation created by Wolfram for its Mathematica language and other services.
Their landing page at reference.wolfram.com/language/ is a good place to start.