[texhax] plain TeX home made symbols for the numbers sets

[Rodolfo Medina]

In the TeXbook, the symbol for the real numbers set is something like:

 ${\rm I\!R}$

Then , the symbol for the natural numbers set can be:

 ${\rm I\!N}$

Can anybody suggest how to get something similar for the integers and rational
numbers sets?

Thanks for any help
Rodolfo