# Why cmmib10 font is not available in stripped down versions of TeX?

In TeXbook p.156 it is said:

Suppose that you want to extend plain TEX by putting boldface math italic letters in family 9, analogous to the normal math italic letters in family 1. (Such fonts aren’t available in stripped down versions of TEX, but let’s assume that they exist.)

`plain.tex` contains this:

``````\font\preloaded=cmmib10 % bold math italic
``````

Considering the fact that `plain.tex` cannot be changed, I don't understand how (and why) this font may not be available in some versions of TeX.

• Possible duplicate of Knuth “Some Implementations of TeX”… – Henri Menke Jul 19 '19 at 2:38
• @HenriMenke The question was asked because the last sentence in this quote from TeXbook is rather confusing. I don't see the point: why "such" fonts may not be available, and "normal math italic" must be available? Therefore, the link that you provided does not answer my question at all. – Igor Liferenko Jul 19 '19 at 3:08
• The point I wanted to make by marking this a duplicate is that such a stripped down version of TeX does not exist, but Knuth assumed that there potentially could exist such a version. And since bold math italics are not too essential for typesetting a hypothetical stripped down version could leave these out. – Henri Menke Jul 19 '19 at 3:30
• @HenriMenke I think this note is no good. Do you think this note would better be removed, or replaced with "(This font is called cmmib10.)"? – Igor Liferenko Jul 19 '19 at 3:39
• @HenriMenke Also, it is not clear what is "version of TeX". Is it "implementation of TeX" or "distribution of TeX"? – Igor Liferenko Jul 19 '19 at 5:12

From the context I think it is clear that it means (what we would now call) a stripped down distribution of tex rather than an implementation of tex.

isn't accurate: `plain.tex` says you can change this bit of the file
The `plain.tex` files used on different machines can be expected to differ widely with respect to preloaded fonts, since the choice of how many fonts to preload and the selection of the most important fonts depends on local conditions.