diff --git a/lib/KorAP/VirtualCorpus.pm b/lib/KorAP/VirtualCorpus.pm
new file mode 100644
index 0000000..58adc6b
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus.pm
@@ -0,0 +1,104 @@
+package KorAP::VirtualCorpus;
+use strict;
+use warnings;
+
+
+# Get or set name of the VC
+sub name {
+  my $self = shift;
+  unless (@_) {
+    return $self->{name};
+  };
+  $self->{name} = shift;
+  return $self;
+};
+
+
+# Comment
+sub comment {
+  my $self = shift;
+  unless (@_) {
+    return $self->{comment};
+  };
+  $self->{comment} //= [];
+
+  push @{$self->{comment}}, @_;
+  return $self;
+};
+
+
+# Flatten the object - can be overwritten
+sub flatten {
+  shift;
+};
+
+
+# Serialize to koral object - can be overwritten
+sub to_koral {
+  shift;
+};
+
+
+# Quote utility function
+sub quote {
+  shift;
+  my $str = shift;
+  $str =~ s/(["\\])/\\$1/g;
+  return qq{"$str"};
+};
+
+
+# Escaped quote utility function
+sub equote {
+  shift;
+  my $str = shift;
+  $str =~ s/(["\\])/\\$1/g;
+  $str =~ s/(["\\])/\\$1/g;
+  return '\\"' . $str . '\\"';
+};
+
+
+sub _commentparam_to_string {
+  my $self = shift;
+  my $comment = $self->_comment_to_string;
+  if ($comment) {
+    return qq!,"comment":"$comment"!;
+  };
+  return '';
+};
+
+
+sub _comment_to_string {
+  my $self = shift;
+  if (!$self->name && !$self->comment) {
+    return '';
+  };
+
+  my $json = '';
+  $json .= 'name:' . $self->equote($self->name) if $self->name;
+  if ($self->name && $self->comment) {
+    $json .= ','
+  };
+  $json .= join(',', @{$self->{comment}}) if $self->{comment};
+
+  return $json;
+};
+
+
+# Stringify collection
+sub to_string {
+  my $self = shift;
+  ## Create collection object
+
+  my $obj = $self->to_koral;
+
+  my $json = '{';
+  $json .= '"@context":"http://korap.ids-mannheim.de/ns/KoralQuery/v0.3/context.jsonld",';
+  $json .= '"collection":';
+  $json .= $obj->_to_fragment;
+  # Set at the end, when all comments are done
+  $json .= $obj->_commentparam_to_string;
+  return $json .= '}';
+};
+
+1;
diff --git a/lib/KorAP/VirtualCorpus/And.pm b/lib/KorAP/VirtualCorpus/And.pm
new file mode 100644
index 0000000..613710b
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus/And.pm
@@ -0,0 +1,69 @@
+package KorAP::VirtualCorpus::And;
+use strict;
+use warnings;
+use base 'KorAP::VirtualCorpus';
+
+
+# TODO:
+#   Support comments!
+
+
+# Constructor
+sub new {
+  my $class = shift;
+  bless { ops => [@_] }, $class;
+};
+
+
+# Get koral type
+sub koral_type {
+  return 'And';
+};
+
+
+# Get operands
+sub operands {
+  shift->{ops};
+};
+
+
+# Flatten group
+sub flatten {
+  my $self = shift;
+
+  my @ops;
+
+  foreach (@{$self->{ops}}) {
+    if ($_->koral_type eq 'And') {
+      push @ops, @{$_->operands};
+    }
+
+    else {
+      push @ops, $_->flatten;
+    };
+  };
+
+  $self->{ops} = \@ops;
+
+  return $self;
+};
+
+
+# Serialize fragment
+sub _to_fragment {
+  my $self = shift;
+  my $json = '{';
+  $json .= '"@type":"koral:docGroup",';
+  $json .= '"operation":"operation:and",';
+  $json .= '"operands":[';
+  $json .= join(',', map { $_->_to_fragment } @{$self->{ops}});
+  $json .= ']';
+
+  # Set at the end, when all comments are done
+  $json .= $self->_commentparam_to_string;
+  $json .= '}';
+  return $json;
+};
+
+
+1;
diff --git a/lib/KorAP/VirtualCorpus/Doc.pm b/lib/KorAP/VirtualCorpus/Doc.pm
new file mode 100644
index 0000000..e635d3d
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus/Doc.pm
@@ -0,0 +1,96 @@
+package KorAP::VirtualCorpus::Doc;
+use strict;
+use warnings;
+use base 'KorAP::VirtualCorpus';
+
+# Constructor
+sub new {
+  my $class = shift;
+  bless {
+    key => shift,
+    match => 'eq',
+    type => 'string',
+    value => ''
+  }, $class;
+};
+
+
+# Clone document VC
+sub clone {
+  my $self = shift;
+  bless {
+    key =>   $self->{key},
+    match => $self->{match},
+    type =>  $self->{type},
+    value => $self->{value},
+  }, __PACKAGE__;
+};
+
+
+# Return object type
+sub koral_type {
+  return 'Doc';
+};
+
+
+# Get or set type
+sub type {
+  my $self = shift;
+  if (@_) {
+    $self->{type} = shift;
+    return $self;
+  };
+  return $self->{type};
+};
+
+
+# Get or set match
+sub match {
+  my $self = shift;
+  if (@_) {
+    $self->{match} = shift;
+    return $self;
+  };
+  return $self->{match};
+};
+
+
+# Get or set key
+sub key {
+  my $self = shift;
+  if (@_) {
+    $self->{key} = shift;
+    return $self;
+  };
+  return $self->{key};
+};
+
+
+# Get or set value
+sub value {
+  my $self = shift;
+  if (@_) {
+    $self->{value} = shift;
+    return $self;
+  };
+  return $self->{value};
+};
+
+
+# Stringify fragment
+sub _to_fragment {
+  my $self = shift;
+  my $json = '{';
+  $json .= '"@type":"koral:doc",';
+  $json .= '"type":"type:' . $self->type . '",';
+  $json .= '"match":"match:' . $self->match . '",';
+  $json .= '"key":"' . $self->key . '",';
+  $json .= '"value":' . $self->quote($self->value);
+
+  # Set at the end, when all comments are done
+  $json .= $self->_commentparam_to_string;
+  return $json . '}';
+};
+
+
+1;
diff --git a/lib/KorAP/VirtualCorpus/DocVec.pm b/lib/KorAP/VirtualCorpus/DocVec.pm
new file mode 100644
index 0000000..49fefb8
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus/DocVec.pm
@@ -0,0 +1,48 @@
+package KorAP::VirtualCorpus::DocVec;
+use strict;
+use warnings;
+use base 'KorAP::VirtualCorpus::Doc';
+
+# Constructor
+sub new {
+  my $class = shift;
+  bless {
+    key => shift,
+    match => 'eq',
+    type => 'string',
+    value => []
+  }, $class;
+};
+
+# Return object type
+sub koral_type {
+  return 'DocVec';
+};
+
+# Get or set value
+sub value {
+  my $self = shift;
+  if (@_) {
+    $self->{value} = [@_];
+    return $self;
+  };
+  return $self->{value};
+};
+
+# Stringify fragment
+sub _to_fragment {
+  my $self = shift;
+  my $json = '{';
+  $json .= '"@type":"koral:doc",';
+  $json .= '"type":"type:' . $self->type . '",';
+  $json .= '"match":"match:' . $self->match . '",';
+  $json .= '"key":"' . $self->key . '",';
+  $json .= '"value":[' . join(',', map { $self->quote($_) } @{$self->value}) . ']';
+
+  # Set at the end, when all comments are done
+  $json .= $self->_commentparam_to_string;
+  return $json . '}';
+};
+
+
+1;
diff --git a/lib/KorAP/VirtualCorpus/Group.pm b/lib/KorAP/VirtualCorpus/Group.pm
new file mode 100644
index 0000000..4062cf9
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus/Group.pm
@@ -0,0 +1,159 @@
+package KorAP::VirtualCorpus::Group;
+use strict;
+use warnings;
+use base 'KorAP::VirtualCorpus';
+use KorAP::VirtualCorpus::Doc;
+use KorAP::VirtualCorpus::And;
+use KorAP::VirtualCorpus::Or;
+
+# Abstract KoralQuery object that normalize to And or Or.
+
+# Construct a new VC group
+sub new {
+  my $class = shift;
+  bless {
+    # New try
+    ops => undef,
+    type => undef
+  }, $class;
+};
+
+
+# Clone object
+sub clone {
+  my $self = shift;
+  my $clone = {};
+  $clone->{ops} = [@{$self->{ops}}] if $self->{ops};
+  $clone->{type} = $self->{type};
+  $clone->{name} = $self->{name};
+  bless $clone, __PACKAGE__;
+};
+
+
+# Add operand
+sub add {
+  my ($self, $type, $op) = @_;
+
+  if (!$self->{ops}) {
+    push @{$self->{ops}}, $op;
+    return $self;
+  };
+
+  if (!$self->{type}) {
+    push @{$self->{ops}}, $op;
+    $self->{type} = $type;
+    return $self;
+  };
+
+  if ($self->{type} eq $type) {
+    push @{$self->{ops}}, $op;
+    return $self;
+  };
+
+  if ($self->{type} eq 'union') {
+    my $vc = KorAP::VirtualCorpus::Or->new(
+      @{$self->{ops}}
+    );
+
+    $self->{type} = 'joint';
+    $self->{ops} = [$vc, $op];
+    return $self;
+  };
+
+  my $vc = KorAP::VirtualCorpus::And->new(
+    @{$self->{ops}}
+  );
+
+  $self->{type} = 'union';
+  $self->{ops} = [$vc, $op];
+  return $self;
+};
+
+
+# Serialize to koral
+sub to_koral {
+  my $self = shift;
+
+  # Single object
+  if (@{$self->{ops}} == 1) {
+    return $self->{ops}->[0]->name($self->name)->flatten;
+  };
+
+  # Union group
+  if ($self->{type} eq 'union') {
+    return KorAP::VirtualCorpus::Or->new(
+      @{$self->{ops}}
+    )->name($self->name)->flatten;
+  }
+
+  # Joint group
+  elsif ($self->{type} eq 'joint') {
+    return KorAP::VirtualCorpus::And->new(
+      @{$self->{ops}}
+    )->name($self->name)->flatten;
+  };
+};
+
+
+# Define an operand to be "or"ed
+sub union {
+  my $self = shift;
+  $self->add('union', shift)
+};
+
+
+# Define a field that should be "or"ed
+sub union_field {
+  my $self = shift;
+  my $field = shift;
+  my $value = shift;
+  $self->union(
+    KorAP::VirtualCorpus::Doc->new($field)->value($value)
+  );
+};
+
+# Define an operand to be "and"ed
+sub joint {
+  my $self = shift;
+  $self->add('joint', shift)
+};
+
+
+# Define a field that should be "and"ed
+sub joint_field {
+  my $self = shift;
+  my $field = shift;
+  my $value = shift;
+  $self->joint(
+    KorAP::VirtualCorpus::Doc->new($field)->value($value)
+    );
+};
+
+
+# Restrict VC by date
+sub from {
+  my $self = shift;
+  my ($year, $month) = @_;
+  my $doc = KorAP::VirtualCorpus::Doc->new('createDate')
+    ->type('date')
+    ->match('geq')
+    ->value($year . '-' . $month);
+  $self->joint($doc);
+};
+
+
+# Restrict VC by date
+sub to {
+  my $self = shift;
+  my ($year, $month) = @_;
+  my $doc = KorAP::VirtualCorpus::Doc->new('createDate')
+    ->type('date')
+    ->match('leq')
+    ->value($year . '-' . $month);
+  $self->joint($doc);
+};
+
+
+1;
+
+__END__
diff --git a/lib/KorAP/VirtualCorpus/Or.pm b/lib/KorAP/VirtualCorpus/Or.pm
new file mode 100644
index 0000000..a795ed3
--- /dev/null
+++ b/lib/KorAP/VirtualCorpus/Or.pm
@@ -0,0 +1,86 @@
+package KorAP::VirtualCorpus::Or;
+use strict;
+use warnings;
+use KorAP::VirtualCorpus::DocVec;
+use base 'KorAP::VirtualCorpus';
+
+
+# TODO:
+#   Support comments!
+
+
+# Constructor
+sub new {
+  my $class = shift;
+  bless { ops => [@_] }, $class;
+};
+
+
+# Get koral type
+sub koral_type {
+  return 'Or';
+};
+
+
+# Get operands
+sub operands {
+  shift->{ops};
+};
+
+
+# Flatten the group
+sub flatten {
+  my $self = shift;
+  my %fields = ();
+  my @ops;
+
+  foreach (@{$self->{ops}}) {
+    if ($_->koral_type eq 'Doc') {
+      if ($_->type eq 'string' && $_->match eq 'eq') {
+        $fields{$_->key} //= [];
+        push @{$fields{$_->key}}, $_->value;
+      };
+    }
+    elsif ($_->koral_type eq 'DocVec') {
+      $fields{$_->key} //= [];
+      push @{$fields{$_->key}}, @{$_->value};
+    }
+    elsif ($_->koral_type eq 'Or') {
+      push @ops, @{$_->operands}
+    }
+    else {
+      push @ops, $_->flatten;
+    }
+  };
+
+  # Vectorize fields
+  foreach (sort keys %fields) {
+    push @ops, KorAP::VirtualCorpus::DocVec->new($_)->value(@{$fields{$_}});
+  };
+
+  if (@ops == 1) {
+    return $ops[0]->name($self->name);
+  };
+
+  $self->{ops} = \@ops;
+  return $self;
+};
+
+
+# Serialize to fragment
+sub _to_fragment {
+  my $self = shift;
+  my $json = '{';
+  $json .= '"@type":"koral:docGroup",';
+  $json .= '"operation":"operation:or",';
+  $json .= '"operands":[';
+  $json .= join(',', map { $_->_to_fragment } @{$self->{ops}});
+  $json .= ']';
+  # Set at the end, when all comments are done
+  $json .= $self->_commentparam_to_string;
+  $json .= '}';
+  return $json;
+};
+
+
+1;
diff --git a/list2vc.pl b/list2vc.pl
index 35a205a..3e31e50 100755
--- a/list2vc.pl
+++ b/list2vc.pl
@@ -1,251 +1,13 @@
 #!/usr/bin/env perl
-package KorAP::VirtualCorpus;
 use strict;
 use warnings;
-
-
-# Get or set name of the VC
-sub name {
-  my $self = shift;
-  unless (@_) {
-    return $self->{name};
-  };
-  $self->{name} = shift;
-  return $self;
-};
-
-
-# Comment
-sub comment {
-  my $self = shift;
-  unless (@_) {
-    return $self->{comment};
-  };
-  $self->{comment} //= [];
-
-  push @{$self->{comment}}, shift;
-  return $self;
-};
-
-
-# Quote utility function
-sub quote {
-  shift;
-  my $str = shift;
-  $str =~ s/(["\\])/\\$1/g;
-  return qq{"$str"};
-};
-
-
-# Escaped quote utility function
-sub equote {
-  shift;
-  my $str = shift;
-  $str =~ s/(["\\])/\\$1/g;
-  $str =~ s/(["\\])/\\$1/g;
-  return '\\"' . $str . '\\"';
-};
-
-
-sub _commentparam_to_string {
-  my $self = shift;
-  my $comment = $self->_comment_to_string;
-  if ($comment) {
-    return qq!,"comment":"$comment"!;
-  };
-  return '';
-};
-
-
-sub _comment_to_string {
-  my $self = shift;
-  if (!$self->name && !$self->comment) {
-    return '';
-  };
-
-  my $json = '';
-  $json .= 'name:' . $self->equote($self->name) if $self->name;
-  if ($self->name && $self->comment) {
-    $json .= ','
-  };
-  $json .= join(',', @{$self->{comment}}) if $self->{comment};
-
-  return $json;
-};
-
-
-# Stringify globally
-sub to_string {
-  my $self = shift;
-  ## Create collection object
-
-  my $json = '{';
-  $json .= '"@context":"http://korap.ids-mannheim.de/ns/KoralQuery/v0.3/context.jsonld",';
-  $json .= '"collection":';
-  $json .= $self->_to_fragment;
-  # Set at the end, when all comments are done
-  $json .= $self->_commentparam_to_string;
-  return $json .= '}';
-};
-
-
-package KorAP::VirtualCorpus::Group;
-use strict;
-use warnings;
-use base 'KorAP::VirtualCorpus';
-
-
-# Construct a new VC group
-sub new {
-  my $class = shift;
-  bless {
-    with => [],
-    with_fields => {},
-    without => [],
-    without_fields => {},
-  }, $class;
-};
-
-
-# Define an operand to be "or"ed
-sub with {
-  my $self = shift;
-  push @{$self->{with}}, shift;
-};
-
-
-# Define a field that should be "or"ed
-sub with_field {
-  my $self = shift;
-  my $field = shift;
-  push @{$self->{with_fields}->{$field}}, shift;
-};
-
-# Define an operand to be "and"ed
-sub without {
-  my $self = shift;
-  push @{$self->{without}}, shift;
-};
-
-
-# Define a field that should be "and"ed
-sub without_field {
-  my $self = shift;
-  my $field = shift;
-  push @{$self->{without_fields}->{$field}}, shift;
-};
-
-
-# VC contains only with fields
-sub only_with_fields {
-  my $self = shift;
-
-  if (keys %{$self->{without_fields}} || @{$self->{with}} || @{$self->{without}}) {
-    return 0;
-  };
-
-  return 1;
-};
-
-
-# Create a document vector field
-sub _doc_vec {
-  my $field = shift;
-  my $vec = shift;
-  my $json = '{';
-  $json .= '"@type":"koral:doc",';
-  $json .= '"key":"' . $field . '",';
-  $json .= '"match":"match:eq",';
-  $json .= '"value":[';
-  $json .= join ',', map { '"' . $_ . '"' } @$vec;
-  $json .=  ']';
-  $json .= '},';
-  return $json;
-}
-
-
-# Stringify fragment
-sub _to_fragment {
-  my $self = shift;
-
-  my $json = '{';
-  $json .= '"@type":"koral:docGroup",';
-
-  # Make the outer group "and"
-  if (keys %{$self->{without_fields}}) {
-    $json .= '"operation":"operation:and",';
-    $json .= '"operands":[';
-
-    foreach my $field (sort keys %{$self->{without_fields}}) {
-      unless (@{$self->{without_fields}->{$field}}) {
-        next;
-      };
-      $json .= _doc_vec($field, $self->{without_fields}->{$field});
-    };
-
-    # Remove the last comma
-    chop $json;
-
-    $json .= ']';
-  }
-
-  elsif (keys %{$self->{with_fields}} || @{$self->{with}}) {
-    $json .= '"operation":"operation:or",';
-
-    $json .= '"operands":[';
-
-    # Flatten embedded "or"-VCs
-    foreach my $op (@{$self->{with}}) {
-
-      # The embedded VC has only extending fields
-      if ($op->only_with_fields) {
-
-        $self->comment('embed:[' . $op->_comment_to_string . ']');
-
-        foreach my $k (keys %{$op->{with_fields}}) {
-          foreach my $v (@{$op->{with_fields}->{$k}}) {
-            $self->with_field($k, $v);
-          };
-        };
-      }
-
-      # Embed complex VC
-      else {
-        $json .= $op->_to_fragment . ',';
-      };
-    };
-
-    foreach my $field (sort keys %{$self->{with_fields}}) {
-      unless (@{$self->{with_fields}->{$field}}) {
-        next;
-      };
-      $json .= _doc_vec($field, $self->{with_fields}->{$field});
-    };
-
-    # Remove the last comma
-    chop $json;
-
-    $json .= ']';
-  }
-
-  # No operands in the group
-  else {
-    # Remove the last comma after the comment
-    chop $json;
-  };
-
-  # Set at the end, when all comments are done
-  $json .= $self->_commentparam_to_string;
-  return $json . '}';
-};
-
-
-package main;
-use strict;
-use warnings;
+use lib 'lib';
+use KorAP::VirtualCorpus::Group;
 
 # 2020-05-20
 #   Preliminary support for C2 def-files.
+# 2020-05-29
+#   Introduce optimizable object system.
 
 our @ARGV;
 
@@ -352,24 +114,24 @@
 
     # Convert C2 sigle to KorAP form
     $value =~ s!^([^/]+?/[^\.]+?)\.(.+?)$!$1\/$2!;
-    ${$vc}->with_field(textSigle => $value);
+    ${$vc}->union_field(textSigle => $value);
   }
 
   # Add doc field
   elsif ($key eq 'doc') {
-    ${$vc}->with_field(docSigle => $value);
+    ${$vc}->union_field(docSigle => $value);
   }
 
   # Add corpus field
   elsif ($key eq 'corpus') {
-    ${$vc}->with_field(corpusSigle => $value);
+    ${$vc}->union_field(corpusSigle => $value);
   }
 
   # Add corpus field
   elsif ($key eq 'cn') {
     # Korpussigle, z.B. 'F97 Frankfurter Allgemeine 1997'
     if ($value =~ m!^([^\/\s]+)(?:\s.+?)?$!) {
-      ${$vc}->with_field(corpusSigle => $1);
+      ${$vc}->union_field(corpusSigle => $1);
     };
   }
 
@@ -430,19 +192,108 @@
       next;
     };
 
-    $$vc->with($all_vcs{$value});
+    $$vc->union($all_vcs{$value}->clone->to_koral);
   }
 
+  # AND definition
+  elsif ($key eq 'and') {
+    unless (defined $all_vcs{$value}) {
+      #       warn 'VC ' . $value . ' not defined';
+      # exit(1);
+      next;
+    };
+
+    $$vc->joint($all_vcs{$value}->clone->to_koral);
+  }
+
+  # Source of the corpus
+  elsif ($key eq 'ql') {
+    # Quellenname, z.B. "Neue Zürcher Zeitung"
+    $$vc->union_field(corpusTitle => $value);
+  }
+
+  elsif ($key eq 'sub') {
+    # "Sub" is the difference - it is the "and not" operation.
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'co') {
+    # Country,	z.B. DE für Text in Deutschland erschienen
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'tl') {
+    # Textlength, Bereich von Texten der angegebenen Länge [in Anz. Wörtern]
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'ts') {
+    # Textsorte, 	z.B. "Bericht"
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'th') {
+    # Thema, z.B. "Sport - Fußball"
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'red') {
+    # Reduktionsfaktor
+    # Wert zw. 1-99%: virt. Korpus wird auf diesen Wert
+    # reduziert. Modus: feste Reduzierung, nicht variabel.
+    warn $key . ' is not yet supported';
+  }
+
+  elsif ($key eq 'thprob') {
+    # ThemaProbability
+    # Wert, der für <th>Thema verwendet wird um zu bestimmen, ab welchem
+    # Zuverläßigkeitswert ein Thema übernommen wird
+  }
+
+
   # Add reduction value as a comment
   elsif ($key eq 'redabs') {
     # "red. Anz. Texte
     # absoluter Wert der durch Reduktion zu erzielende Anzahl Texte"
     $$vc->comment('redabs:' . $value);
+    warn $key . ' is not yet supported';
+  }
+
+  # Add reduction value as a comment
+  elsif ($key eq 'date') {
+    # Supports two pattern schemes:
+    # m1=Year1/Month1 bis Year2/Month2
+    #   Datumsbereich Schema 1: z.B. "2000/01 bis 2010/12"
+
+    # Schema 1
+    if ($value =~ m!^(?:m1\s*=\s*)?\s*(\d+)\/(\d+) bis (\d+)\/(\d+)\s*$!s) {
+      my ($y1, $m1, $y2, $m2) = ($1, $2, $3, $4);
+      if ($m1 < 10) {
+        $m1 = '0' . (0+$m1);
+      };
+      if ($m2 < 10) {
+        $m2 = '0' . (0+$m2);
+      };
+      $$vc->from($y1, $m1);
+      $$vc->to($y2, $m2);
+    }
+
+    # Scheme 2
+    elsif ($value =~ m!^\s*\d{4}-\d{4}\s+und\s+\d{1,2}-\d{1,2}\s*$!) {
+      # m2=Year1-Year2 und Month1-Month2
+      #   Datumsbereich Schema 2: z.B. "1990-2000 und 06-06"
+
+      warn 'Second date scheme not yet supported!'
+    }
+
+    else {
+      warn 'Unknown date scheme ' . $value;
+    };
   }
 
   # Unknown
   else {
-    # warn $key . ' is an unknown field';
+    warn $key . ' is an unknown field';
   };
 };
 
diff --git a/t/list2vc-def.t b/t/list2vc-def.t
index baaefda..a3b60e7 100644
--- a/t/list2vc-def.t
+++ b/t/list2vc-def.t
@@ -44,38 +44,41 @@
 
 my $list3 = catfile(dirname(__FILE__), 'data', 'list3.def');
 
+
 # Check JSON
 # Only return extended area
 $json = decode_json(join('', `$script $list3`));
 
-is($json->{'collection'}->{'@type'}, 'koral:docGroup', 'type');
-is($json->{'collection'}->{'operation'}, 'operation:or', 'operation');
+is($json->{'collection'}->{'@type'}, 'koral:doc', 'type');
+
+
 is($json->{'collection'}->{'comment'}, 'name:"VAS-N91 (Stand \"2013\", korr. 2017)"', 'type');
 
-$op1 = $json->{'collection'}->{'operands'}->[0];
+$op1 = $json->{'collection'};
 is($op1->{'@type'}, 'koral:doc', 'type');
 is($op1->{'key'}, 'textSigle', 'key');
 is($op1->{'match'}, 'match:eq', 'match');
 is($op1->{'value'}->[0], "A00/APR/23232", 'value');
 is($op1->{'value'}->[1], "A00/APR/23233", 'value');
 
-
 my $list4 = catfile(dirname(__FILE__), 'data', 'list4.def');
 
 # Only contains intended area
 $json = decode_json(join('', `$script $list4`));
 
 is($json->{'collection'}->{'@type'}, 'koral:docGroup', 'type');
-is($json->{'collection'}->{'operation'}, 'operation:or', 'operation');
+is($json->{'collection'}->{'comment'}, 'name:"VAS N91"', 'name');
 like($json->{'collection'}->{'comment'}, qr!^name:"VAS N91"!, 'name');
-like($json->{'collection'}->{'comment'}, qr!embed:\[name:"Berliner Zeitung",redabs:143237\]!, 'embed');
-like($json->{'collection'}->{'comment'}, qr!embed:\[name:"Frankfurter Allgemeine",redabs:301166\]!, 'embed');
 
-$op1 = $json->{'collection'}->{'operands'}->[0];
-is($op1->{'@type'}, 'koral:doc', 'type');
-is($op1->{'key'}, 'corpusSigle', 'key');
-is($op1->{'match'}, 'match:eq', 'match');
-is($op1->{'value'}->[0], "F97", 'value');
-is($op1->{'value'}->[1], "F99", 'value');
+
+my $bz = $json->{'collection'}->{operands}->[0]->{operands}->[0];
+is($bz->{operation}, 'operation:and', 'Intersection');
+is(scalar @{$bz->{operands}}, 3, 'Flatten operands');
+
+my $faz = $json->{'collection'}->{operands}->[0]->{operands}->[1];
+is($faz->{'@type'}, 'koral:doc', 'DocVec');
+is($faz->{value}->[0], 'F97', 'Value');
+is($faz->{value}->[1], 'F99', 'Value');
 
 done_testing;
+__END__
diff --git a/t/list2vc-obj.t b/t/list2vc-obj.t
new file mode 100644
index 0000000..d4bbd80
--- /dev/null
+++ b/t/list2vc-obj.t
@@ -0,0 +1,23 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use Test::More;
+use Data::Dumper;
+use Mojo::JSON 'decode_json';
+
+require_ok 'KorAP::VirtualCorpus::Group';
+
+my $vc = KorAP::VirtualCorpus::Group->new;
+$vc->union_field('author', 'Goethe');
+$vc->union_field('author', 'Schiller');
+$vc->joint_field('author', 'Fontane');
+
+
+my $json = decode_json $vc->to_koral->to_string;
+
+is($json->{collection}->{operation}, 'operation:and');
+is($json->{collection}->{operands}->[0]->{'@type'}, 'koral:doc');
+is($json->{collection}->{operands}->[0]->{'value'}->[0], 'Goethe');
+is($json->{collection}->{operands}->[0]->{'value'}->[1], 'Schiller');
+
+done_testing;