t := C(t1,...,tn) | C | n | "ccc" | r | [t1,....,tn]
where n stands for the decimal numbers, "ccc" for a string, r for a real.
The ATermLibrary implements the internal representation of ATerms and the conversion between the external and the internal representation. ATerms can also
be represented in an efficient binary format in which complete sharing of subterms is maintained.