code: ///////////////////////////////////////////////////////////////////////////
  //                   __                _      _   ________               //
  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed under the Apache License, Version 2.0 (the "License");      //
  //  you may not use this file except in compliance with the License.     //
  //  You may obtain a copy of the License at                              //
  //                                                                       //
  //  http://www.apache.org/licenses/LICENSE-2.0                           //
  //                                                                       //
  //  Unless required by applicable law or agreed to in writing, software  //
  //  distributed under the License is distributed on an "AS IS" BASIS,    //
  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
  //  implied.  See the License for the specific language governing        //
  //  permissions and limitations under the License.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.formulas.printer;
  
  import org.logicng.formulas.CType;
  import org.logicng.formulas.FType;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.Literal;
  
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  /**
   * The UTF8 string representation for formulas.
   * @version 1.1
   * @since 1.0
   */
  public final class UTF8StringRepresentation extends FormulaStringRepresentation {
  
      private static final Pattern pattern = Pattern.compile("(.*?)(\\d*)");
  
      /**
       * Returns the UTF8 string for a variable name
       * @param name the name
       * @return the matching UTF8 symbol
       */
      private static String utf8Name(final String name) {
          final Matcher matcher = pattern.matcher(name);
          if (!matcher.matches()) {
              return name;
          }
          if (matcher.group(2).isEmpty()) {
              return matcher.group(1);
          }
          return matcher.group(1) + getSubscript(matcher.group(2));
      }
  
      private static String getSubscript(final String number) {
          final StringBuilder sb = new StringBuilder();
          for (final char c : number.toCharArray()) {
              switch (c) {
                  case '0':
                      sb.append("₀");
                      break;
                  case '1':
                      sb.append("₁");
                      break;
                  case '2':
                      sb.append("₂");
                      break;
                  case '3':
                      sb.append("₃");
                      break;
                  case '4':
                      sb.append("₄");
                      break;
                  case '5':
                      sb.append("₅");
                      break;
                  case '6':
                      sb.append("₆");
                      break;
                  case '7':
                      sb.append("₇");
                      break;
                  case '8':
                      sb.append("₈");
                      break;
                  case '9':
                      sb.append("₉");
                      break;
                  default:
                      break;
              }
          }
          return sb.toString();
      }
  
      @Override
      protected String toInnerString(final Formula formula) {
          if (formula.type() == FType.LITERAL) {
              final Literal lit = (Literal) formula;
              return lit.phase() ? utf8Name(lit.name()) : this.negation() + utf8Name(lit.name());
          }
          return super.toInnerString(formula);
      }
  
      @Override
      protected String falsum() {
          return "⊥";
      }
  
      @Override
      protected String verum() {
          return "⊤";
      }
  
      @Override
      protected String negation() {
          return "¬";
      }
  
      @Override
      protected String implication() {
          return " ⇒ ";
      }
  
      @Override
      protected String equivalence() {
          return " ⇔ ";
      }
  
      @Override
      protected String and() {
          return " ∧ ";
      }
  
      @Override
      protected String or() {
          return " ∨ ";
      }
  
      @Override
      protected String pbComparator(CType comparator) {
          switch (comparator) {
              case EQ:
                  return " = ";
              case LE:
                  return " ≤ ";
              case LT:
                  return " < ";
              case GE:
                  return " ≥ ";
              case GT:
                  return " > ";
              default:
                  throw new IllegalArgumentException("Unknown pseudo-Boolean comparison: " + comparator);
          }
      }
  
      @Override
      protected String pbMul() {
          return "";
      }
  
      @Override
      protected String pbAdd() {
          return " + ";
      }
  
      @Override
      protected String lbr() {
          return "(";
      }
  
      @Override
      protected String rbr() {
          return ")";
      }
  
      @Override
      public String toString() {
          return this.getClass().getSimpleName();
      }
  }
  