Basic version of my question: Consider the fragment of some text
bla bla $x_1,x_2,x_3$ bla. Is this correctly type-setted, or is
bla bla $x_1$, $x_2$, $x_3$ bla better ?
Advanced version: Cf. the "Chicago Manual of Style", 16th printed ed, on pp. 589, in 12.19 it is recommended that typesetting lists of mathematical symbols, e.g.
$x_1,x_2,x_3$ that medium spaces between commas should be used. Does LaTeX insert these automatically ? If not, should I use
$x_1\:,x_2,\:x_3$ rather than
$x_1$, $x_2$, $x_3$ ? It appears that these strings differ slightly in length, when the document is compiled to pdf.