code: SourcedToken getEquivalentToken(Token tok) {
          if (unsourcedTokens.contains(tok.getValue())) {
              for (int i=0; i<tokens.length; i++) {
                  if (tokens[i].getValue().equals(tok.getValue())) {
                      return tokens[i];
                  }
              }
              System.out.println("This is a problem");
              return null;
          } else {
              return null;
          }
      }
docs: Test if this token appears at least once.