function previousIssue () {
  var url     = document.location.toString ();
  url         = url.replace (/#$/, "");
  var pattern = /\/v(\d+)n((\d+|-|s)+).html$/;
  var capture = url.match (pattern);
  if (capture != null) {
    var volume = capture[1];
    var issue  = capture[2];
    if (volume == 14 && issue == 1) {
      issue = "s1";
    } else if (volume == 14 && issue == "s1") {
      volume = 13;
      issue  = 4;
    } else if (volume == 13 && issue == 1) {
      issue = "s";
    } else if (volume == 13 && issue == "s") {
      volume = 12;
      issue  = 4;
    } else if (volume == 8 && issue == 1) {
      issue = "s";
    } else if (volume == 8 && issue == "s") {
      volume = 7;
      issue  = "3-4";
    } else if (volume == 7 && issue == "3-4") {
      issue = 2;
    } else if (volume == 5 && issue == 1) {
      issue = "s";
    } else if (volume == 5 && issue == "s") {
      volume = 4;
      issue  = 4;
    } else if (volume == 2 && issue == 1) {
      issue = "s";
    } else if (volume == 2 && issue == "s") {
      volume = 1;
      issue  = 4;
    } else {
      if (issue == 1) {
        volume--;
        issue = 4;
      } else {
        issue--;
      }
    }
    url = url.replace (pattern, "/v" + volume + "n" + issue + ".html");
    document.location = url;
  }
}



function nextIssue () {
  var url     = document.location.toString ();
  url         = url.replace (/#$/, "");
  var pattern = /\/v(\d+)n((\d+|-|s)+).html$/;
  var capture = url.match (pattern);
  if (capture != null) {
    var volume = capture[1];
    var issue  = capture[2];
    if (volume == 1 && issue == 4) {
      volume = 2;
      issue  = "s";
    } else if (volume == 2 && issue == "s") {
      issue = 1;
    } else if (volume == 4 && issue == 4) {
      volume = 5;
      issue  = "s";
    } else if (volume == 5 && issue == "s") {
      issue = 1;
    } else if (volume == 7 && issue == 2) {
      issue = "3-4";
    } else if (volume == 7 && issue == "3-4") {
      volume = 8;
      issue  = "s";
    } else if (volume == 8 && issue == "s") {
      issue = 1;
    } else if (volume == 12 && issue == 4) {
      volume = 13;
      issue  = "s";
    } else if (volume == 13 && issue == "s") {
      issue = 1;
    } else if (volume == 13 && issue == 4) {
      volume = 14;
      issue  = "s1";
    } else if (volume == 14 && issue == "s1") {
      issue = 1;
    } else {
      if (issue == 4) {
        volume++;
        issue = 1;
      } else {
        issue++;
      }
    }
    url = url.replace (pattern, "/v" + volume + "n" + issue + ".html");
    document.location = url;
  }
}