code: def add_statements(self, pmid, stmts):
          
          if pmid not in self.stmts:
              self.stmts[pmid] = stmts
          else:
              self.stmts[pmid] += stmts
docs: Add INDRA Statements to the incremental model indexed by PMID.
  
          Parameters
          ----------
          pmid : str
              The PMID of the paper from which statements were extracted.
          stmts : list[indra.statements.Statement]
              A list of INDRA Statements to be added to the model.