#!/usr/bin/awk -f

BEGIN { FS = "\t"; OFS = FS }

1 == NR {
  attributes = $0
  tupleSize = NF
  next
}

1 == FNR {
  if ( $0 != attributes ) {
    printf( "ERROR: %s is not union compatible with previous input.\n", FILENAME ) >>"/dev/stderr"
    printf( "       Expecting \"%s\".\n", attributes ) >>"/dev/stderr"
    printf( "       Got       \"%s\".\n", $0 ) >>"/dev/stderr"
    aborting = 1
    exit 1
  }
  next
}

NF != tupleSize {
  print "ERROR: Wrong tuple size." >>"/dev/stderr"
  aborting = 1
  exit 1
}

{ tuples[$0] = 1 }

END { if ( aborting ) exit 1 }

END {
  print attributes
  for ( r in tuples ) {
    print r
  }
}