anchor.diff:  -record(alteration,
   		{name :: string(),
   		description :: string(),
  -		valid_for	:: {integer(), integer()},
  +		valid_for	:: valid_for(),
   		type :: price_type(),
   		units :: unit_of_measure(),
   		size :: integer(),
  
positive.code: -record(product,
  		{name :: string(),
  		description :: string(),
  		valid_for	:: {integer(), integer()},
  		is_bundle = false :: boolean(),
  		status :: product_status(),
  		start_date :: pos_integer(), % ISO8601
  		termination_date :: pos_integer(), % ISO8601
  		price :: [#price{}]}).
  
negative.code: -record(price,
  		{name :: string(),
  		description :: string(),
  		valid_for	:: valid_for(),
  		type :: price_type(),
  		units :: unit_of_measure(),
  		currency :: undefined | string(),
  		period :: valid_period(),
  		size :: integer(),
  		amount :: integer(),
  