diff --git a/source/api/actions/events.ts b/source/api/actions/events.ts
index ee69555..e85f2c8 100644
--- a/source/api/actions/events.ts
+++ b/source/api/actions/events.ts
@@ -111,8 +111,8 @@ namespace _zeitbild.api
 					const session : {key : string; value : lib_plankton.session.type_session;} = await session_from_stuff(stuff);
 					const user_id : _zeitbild.type_user_id = await _zeitbild.service.user.identify(session.value.name);
 					
-					const from : _zeitbild.helpers.type_pit = parseInt(stuff.query_parameters["from"]);
-					const to : _zeitbild.helpers.type_pit = parseInt(stuff.query_parameters["to"]);
+					const from : lib_plankton.pit.type_pit = parseInt(stuff.query_parameters["from"]);
+					const to : lib_plankton.pit.type_pit = parseInt(stuff.query_parameters["to"]);
 					const calendar_ids_wanted : (null | Array<_zeitbild.type_calendar_id>) = (
 						(
 							("calendar_ids" in stuff.query_parameters)
diff --git a/source/helpers.ts b/source/helpers.ts
index f6965d6..d5b929d 100644
--- a/source/helpers.ts
+++ b/source/helpers.ts
@@ -4,478 +4,12 @@
 namespace _zeitbild.helpers
 {
 	
-	/**
-	 */
-	export function date_object_get_week_of_year(
-		date : Date
-	) : int
-	{
-		let date_ : Date = new Date(date.getTime());
-		date_.setHours(0, 0, 0, 0);
-		// Thursday in current week decides the year.
-		date_.setDate(date_.getDate() + 3 - (date_.getDay() + 6) % 7);
-		// January 4 is always in week 1.
-		let week1 : Date = new Date(date_.getFullYear(), 0, 4);
-		// Adjust to Thursday in week 1 and count number of weeks from date to week1.
-		return (
-			1
-			+
-			Math.round(
-				(
-					((date_.getTime() - week1.getTime()) / 86400000)
-					-
-					3
-					+
-					(week1.getDay() + 6) % 7
-				)
-				/
-				7
-			)
-		);
-	}
-	
-	
-	/**
-	 * @todo unite with type_datetimeobject?
-	 */
-	export type type_datetime = {
-		timezone_shift : int;
-		date : type_date;
-		time : (
-			null
-			|
-			type_time
-		);
-	};
-	
-	
-	/**
-	 * @todo timezone_shift
-	 */
-	function datetime_from_date_object(
-		date : Date,
-		options : {
-			timezone_shift ?: int;
-		} = {}
-	) : type_datetime
-	{
-		options = Object.assign(
-			{
-				"timezone_shift": 0,
-			},
-			options
-		);
-		const date_ : Date = lib_plankton.call.convey(
-			date,
-			[
-				(x : Date) => x.getTime(),
-				(x : int) => (x + (((options.timezone_shift as int) * (60 * 60)) * 1000)),
-				(x : int) => new Date(x),
-			]
-		);
-		const iso_string : string = date_.toISOString();
-		return {
-			"timezone_shift": (options.timezone_shift as int),
-			"date": {
-				"year": parseInt(iso_string.slice(0, 4)),
-				"month": parseInt(iso_string.slice(5, 7)),
-				"day": parseInt(iso_string.slice(8, 10)),
-			},
-			"time": {
-				"hour": parseInt(iso_string.slice(11, 13)),
-				"minute": parseInt(iso_string.slice(14, 16)),
-				"second": parseInt(iso_string.slice(17, 19)),
-			},
-		};
-	}
-	
-	
-	/**
-	 * @todo negative shift?
-	 */
-	function datetime_to_date_object(
-		datetime : type_datetime
-	) : Date
-	{
-		const iso_string : string = lib_plankton.string.coin(
-			"{{year}}-{{month}}-{{day}}T{{hour}}:{{minute}}:{{second}}.000+{{shift}}",
-			{
-				"year": datetime.date.year.toFixed(0).padStart(4, "0"),
-				"month": datetime.date.month.toFixed(0).padStart(2, "0"),
-				"day": datetime.date.day.toFixed(0).padStart(2, "0"),
-				"hour": ((datetime.time !== null) ? datetime.time.hour : 0).toFixed(0).padStart(2, "0"),
-				"minute": ((datetime.time !== null) ? datetime.time.minute : 0).toFixed(0).padStart(2, "0"),
-				"second": ((datetime.time !== null) ? datetime.time.second : 0).toFixed(0).padStart(2, "0"),
-				"shift": (datetime.timezone_shift.toFixed(0).padStart(2, "0") + ":00"),
-			}
-		);
-		return (new Date(iso_string));
-	}
-
-
-	/**
-	 */
-	export type type_pit = int;
-
-
-	/**
-	 */
-	export function pit_to_date_object(
-		pit : type_pit
-	) : Date
-	{
-		return (new Date(pit * 1000));
-	}
-
-
-	/**
-	 */
-	function pit_from_date_object(
-		date_object : Date
-	) : type_pit
-	{
-		return Math.round(date_object.getTime() / 1000);
-	}
-
-
-	/**
-	 */
-	export function pit_now(
-	) : type_pit
-	{
-		return pit_from_date_object(new Date(Date.now()));
-	}
-
-
-	/**
-	 * @todo timezone
-	 */
-	export function pit_to_datetime(
-		pit : type_pit,
-		options : {
-			timezone_shift ?: int
-		} = {}
-	) : type_datetime
-	{
-		options = Object.assign(
-			{
-				"timezone_shift": 0,
-			},
-			options
-		);
-		const date_object : Date = pit_to_date_object(pit);
-		return datetime_from_date_object(
-			date_object,
-			{
-				"timezone_shift": (options.timezone_shift as int),
-			}
-		);
-	}
-
-
-	/**
-	 */
-	export function pit_from_datetime(
-		datetime : type_datetime
-	) : type_pit
-	{
-		return lib_plankton.call.convey(
-			datetime,
-			[
-				datetime_to_date_object,
-				pit_from_date_object,
-			]
-		);
-	}
-
-
-	/**
-	 */
-	export function pit_is_before(
-		pit : type_pit,
-		reference : type_pit
-	) : boolean
-	{
-		return (pit < reference);
-	}
-
-
-	/**
-	 */
-	function pit_is_after(
-		pit : type_pit,
-		reference : type_pit
-	) : boolean
-	{
-		return (pit > reference);
-	}
-
-
-	/**
-	 */
-	export function pit_is_between(
-		pit : type_pit,
-		reference_left : type_pit,
-		reference_right : type_pit
-	) : boolean
-	{
-		return (
-			pit_is_after(pit, reference_left)
-			&&
-			pit_is_before(pit, reference_right)
-		);
-	}
-
-
-	/**
-	 */
-	function pit_shift_hour(
-		pit : type_pit,
-		increment : int
-	) : type_pit
-	{
-		return (pit + (60 * 60 * increment));
-	}
-
-
-	/**
-	 */
-	export function pit_shift_day(
-		pit : type_pit,
-		increment : int
-	) : type_pit
-	{
-		return (pit + (60 * 60 * 24 * increment));
-	}
-
-
-	/**
-	 */
-	export function pit_shift_week(
-		pit : type_pit,
-		increment : int
-	) : type_pit
-	{
-		return (pit + (60 * 60 * 24 * 7 * increment));
-	}
-
-
-	/**
-	 */
-	function pit_shift_year(
-		pit : type_pit,
-		increment : int
-	) : type_pit
-	{
-		return (pit + (60 * 60 * 24 * 365 * increment));
-	}
-
-
-	/**
-	 */
-	function pit_trunc_minute(
-		pit : type_pit
-	) : type_pit
-	{
-		const datetime_input : type_datetime = pit_to_datetime(pit);
-		const datetime_output : type_datetime = {
-			"timezone_shift": 0,
-			"date": {
-				"year": datetime_input.date.year,
-				"month": datetime_input.date.month,
-				"day": datetime_input.date.day,
-			},
-			"time": {
-				"hour": (
-					(datetime_input.time === null)
-					?
-					0
-					:
-					datetime_input.time.hour
-				),
-				"minute": (
-					(datetime_input.time === null)
-					?
-					0
-					:
-					datetime_input.time.minute
-				),
-				"second": 0,
-			},
-		};
-		return pit_from_datetime(datetime_output);
-	}
-
-
-	/**
-	 */
-	function pit_trunc_hour(
-		pit : type_pit
-	) : type_pit
-	{
-		const datetime_input : type_datetime = pit_to_datetime(pit);
-		const datetime_output : type_datetime = {
-			"timezone_shift": 0,
-			"date": {
-				"year": datetime_input.date.year,
-				"month": datetime_input.date.month,
-				"day": datetime_input.date.day,
-			},
-			"time": {
-				"hour": (
-					(datetime_input.time === null)
-					?
-					0
-					:
-					datetime_input.time.hour
-				),
-				"minute": 0,
-				"second": 0,
-			},
-		};
-		return pit_from_datetime(datetime_output);
-	}
-
-
-	/**
-	 */
-	function pit_trunc_day(
-		pit : type_pit
-	) : type_pit
-	{
-		const datetime_input : type_datetime = pit_to_datetime(pit);
-		const datetime_output : type_datetime = {
-			"timezone_shift": 0,
-			"date": {
-				"year": datetime_input.date.year,
-				"month": datetime_input.date.month,
-				"day": datetime_input.date.day,
-			},
-			"time": {
-				"hour": 0,
-				"minute": 0,
-				"second": 0,
-			},
-		};
-		return pit_from_datetime(datetime_output);
-	}
-
-
-	/**
-	 */
-	export function pit_trunc_week(
-		pit : type_pit
-	) : type_pit
-	{
-		const date_object : Date = pit_to_date_object(pit);
-		return lib_plankton.call.convey(
-			date_object.getDay(),
-			[
-				(x : int) => ((x === 0) ? 7 : x),
-				(x : int) => (x - 1),
-				(x : int) => pit_shift_day(pit, (-x)),
-				pit_trunc_day
-			]
-		);
-	}
-
-
-	/**
-	 */
-	function pit_trunc_month(
-		pit : type_pit
-	) : type_pit
-	{
-		const datetime_input : type_datetime = pit_to_datetime(pit);
-		const datetime_output : type_datetime = {
-			"timezone_shift": 0,
-			"date": {
-				"year": datetime_input.date.year,
-				"month": datetime_input.date.month,
-				"day": 1,
-			},
-			"time": {
-				"hour": 0,
-				"minute": 0,
-				"second": 0,
-			},
-		};
-		return pit_from_datetime(datetime_output);
-	}
-
-
-	/**
-	 */
-	function pit_trunc_year(
-		pit : type_pit
-	) : type_pit
-	{
-		const datetime_input : type_datetime = pit_to_datetime(pit);
-		const datetime_output : type_datetime = {
-			"timezone_shift": 0,
-			"date": {
-				"year": datetime_input.date.year,
-				"month": 1,
-				"day": 1,
-			},
-			"time": {
-				"hour": 0,
-				"minute": 0,
-				"second": 0,
-			},
-		};
-		return pit_from_datetime(datetime_output);
-	}
-
-
-	/**
-	 * @param year year according to specified timezone shift
-	 * @param week week according to specified timezone shift
-	 * @return the begin of the week (monday, 00:00)
-	 */
-	export function pit_from_year_and_week(
-		year : int,
-		week : int,
-		options : {
-			timezone_shift ?: int;
-		} = {}
-	) : type_pit
-	{
-		options = Object.assign(
-			{
-				"timezone_shift": 0,
-			},
-			options
-		);
-		return lib_plankton.call.convey(
-			{
-				"timezone_shift": (options.timezone_shift as int),
-				"date": {
-					"year": year,
-					"month": 1,
-					"day": 1,
-				},
-				"time": {
-					"hour": 0,
-					"minute": 0,
-					"second": 0
-				}
-			},
-			[
-				pit_from_datetime,
-				(x : type_pit) => pit_shift_week(x, (week - 1)),
-				pit_trunc_week,
-			]
-		);
-	}
-
-
 	/**
 	 * @todo timezone
 	 */
 	function ical_datetime_to_own_datetime(
 		ical_datetime : lib_plankton.ical.type_datetime
-	) : type_datetime
+	) : lib_plankton.pit.type_datetime
 	{
 		return {
 			"timezone_shift": 0,
@@ -504,7 +38,7 @@ namespace _zeitbild.helpers
 	 */
 	export function ical_dt_to_own_datetime(
 		ical_dt: lib_plankton.ical.type_dt
-	) : type_datetime
+	) : lib_plankton.pit.type_datetime
 	{
 		return {
 			"timezone_shift": 0,
diff --git a/source/repositories/resource.ts b/source/repositories/resource.ts
index 5b0e788..8b4a45b 100644
--- a/source/repositories/resource.ts
+++ b/source/repositories/resource.ts
@@ -184,7 +184,7 @@ namespace _zeitbild.repository.resource
 		stuff : type_local_resource_event_stuff
 	) : Record<string, any>
 	{
-		const encode_datetime : ((datetime : _zeitbild.helpers.type_datetime) => string) = ((datetime) => {
+		const encode_datetime : ((datetime : lib_plankton.pit.type_datetime) => string) = ((datetime) => {
 			return lib_plankton.string.coin(
 				"{{timezone_shift}}|{{date}}{{macro_time}}",
 				{
@@ -237,7 +237,7 @@ namespace _zeitbild.repository.resource
 		row : Record<string, any>
 	) : type_local_resource_event_stuff
 	{
-		const decode_datetime : ((datetime_raw : string) => _zeitbild.helpers.type_datetime) = ((datetime_raw) => {
+		const decode_datetime : ((datetime_raw : string) => lib_plankton.pit.type_datetime) = ((datetime_raw) => {
 			const parts : Array<string> = datetime_raw.split("|");
 			const timezone_shift : int = parseInt(parts[0]);
 			if (parts[1].length <= 10) {
diff --git a/source/services/calendar.ts b/source/services/calendar.ts
index 4baf27e..a8c49c2 100644
--- a/source/services/calendar.ts
+++ b/source/services/calendar.ts
@@ -165,8 +165,8 @@ namespace _zeitbild.service.calendar
 	 */
 	async function get_events(
 		calendar_id : _zeitbild.type_calendar_id,
-		from_pit : _zeitbild.helpers.type_pit,
-		to_pit : _zeitbild.helpers.type_pit,
+		from_pit : lib_plankton.pit.type_pit,
+		to_pit : lib_plankton.pit.type_pit,
 		user_id : _zeitbild.type_user_id
 	) : Promise<
 		Array<
@@ -197,8 +197,8 @@ namespace _zeitbild.service.calendar
 								(events) => Promise.resolve(
 									events
 									.filter(
-										(event : _zeitbild.type_event_object) => _zeitbild.helpers.pit_is_between(
-											_zeitbild.helpers.pit_from_datetime(event.begin),
+										(event : _zeitbild.type_event_object) => lib_plankton.pit.is_between(
+											lib_plankton.pit.from_datetime(event.begin),
 											from_pit,
 											to_pit
 										)
@@ -279,8 +279,8 @@ namespace _zeitbild.service.calendar
 								(event) => (event !== null)
 							)
 							.filter(
-								(event) => _zeitbild.helpers.pit_is_between(
-									_zeitbild.helpers.pit_from_datetime(event.begin),
+								(event) => lib_plankton.pit.is_between(
+									lib_plankton.pit.from_datetime(event.begin),
 									from_pit,
 									to_pit
 								)
@@ -305,8 +305,8 @@ namespace _zeitbild.service.calendar
 	 */
 	export async function gather_events(
 		calendar_ids_wanted : (null | Array<_zeitbild.type_calendar_id>),
-		from_pit : _zeitbild.helpers.type_pit,
-		to_pit : _zeitbild.helpers.type_pit,
+		from_pit : lib_plankton.pit.type_pit,
+		to_pit : lib_plankton.pit.type_pit,
 		user_id : _zeitbild.type_user_id
 	) : Promise<
 		Array<
diff --git a/source/types.ts b/source/types.ts
index d540af5..920de23 100644
--- a/source/types.ts
+++ b/source/types.ts
@@ -35,11 +35,11 @@ namespace _zeitbild
 	 */
 	export type type_event_object = {
 		name : string;
-		begin : _zeitbild.helpers.type_datetime;
+		begin : lib_plankton.pit.type_datetime;
 		end : (
 			null
 			|
-			_zeitbild.helpers.type_datetime
+			lib_plankton.pit.type_datetime
 		);
 		location : (
 			null