vector<X> aas;
vector<X>::iterator aa;
map<K,V> SEQ;
map<K,V>::iterator seq;
vector<Z> codons;
vector<Z>::iterator codon;

for (aa=aas.begin(); aa!=aas.end(); ++aa) {
    for (seq=SEQ.begin(); seq!=SEQ.end(); ++seq) {
        for (codon=codons.begin(); codon!=codons.end(); ++codon) {
                ... do something ...
            }
        }
    }