Unable to assign numbers greater than 20 or less than -20 to an int

[Convindix]

The following code compiles to tm2:

int a;
a = 20;

However, the following does not:

int a;
a = 21;

In general this compiles for all integers between -20 and 20 inclusive. It looks like this is because in the standard library, there are files BUILTIN_assign[n].tmd for n from 1 to 20, and a file BUILTIN_assignNot.tmd which I am guessing handles negative integers. (I am not sure how assignment to 0 is handled.)