[texhax] \noalign{\nobreak} seems not work!

[Rodolfo Medina]

Hi, everybody.

Something strange seems to happen:
In the TeXbook, page 193, it is said that the command
\noalign{\nobreak}
after the \cr in \eqalignno
will prohibit a page break after that line.

I tried it, but it does not seem to work!
Can anyone tell me about this?

On the contrary, 
\noalign{\break}
seems to perfectly work in forcing a page breaking.
I can't explain to myself!

Cheers,
Rodolfo