code: def ascending_sort_key(self):
          
          return (
              len(self.alt_reads_supporting_protein_sequence),
              min(t.number_mismatches_before_variant for t in self.translations),
              min(t.number_mismatches_after_variant for t in self.translations),
              len(self.transcripts_supporting_protein_sequence)
          )
docs: Sort protein sequences lexicographically by three criteria:
              - number of unique supporting reads
              - minimum mismatch versus a supporting reference transcript before variant
              - minimum mismatch versus a supporting reference transcript after variant
              - number of supporting reference transcripts
  
          TODO: Add sort criterion:
              - min number of reads covering each nucleotide of
                the protein sequence >= 2