def self.at_beginning_of_interval(time, interval_type)
      #simple substraction does not (seem) to work for long intervals (summer/winter time ?)
      #and at_beginning_of_hour is not defined
...

def convert_umlaut_to_base(input)
  $KCODE='u'
  %w(aáä AÁÄÅ oóö OÓÖ ií IÍ uúü UÚÜ eé EÉ sß).inject(input.dup) do |input, set|
...

def convert_umlaut_to_base(input)
  $KCODE='u'
  %w( áäa ÁÄÅA óöo ÓÖO íi ÍI úüu ÚÜU ée ÉE ßs ).inject(input.dup) do |input, set|
...

def convert_umlaut_to_base(input)
    text = input.dup
    %w[áäa ÁÄÅA óöo ÓÖO íi ÍI úüu ÚÜU ée ÉE ßs].each do |set|
...