The Ninth Senate had to decide in several proceedings on the consequences of an increase in the weekly compulsory teaching hours for employed teachers in the state of North Rhine-Westphalia (NRW) who were in partial retirement. Anzuwenden waren die Tarifbestimmungen des Öffentlichen Diensts. The working hours of employed teachers are based on No. 3 of the special regulation for employees as teachers (SR2l I BAT). In North Rhine-Westphalia, working hours are regulated by legal regulations; The regular annual average permissible working hours for civil servant teachers in all types of schools was increased by one compulsory teaching hour per week. With judgments of April 11, 38 2006 (- 9 AZR 258/05, 369/05, 368/05, 371/05, 420/05 and 429/05 -) the Ninth Senate decided that the number of compulsory teaching hours of the employed teachers in partial retirement are not increased proportionately. When interpreting a partial retirement agreement, it must be assumed that the parties also want to bring about the social law consequences of a partial retirement agreement with the agreement. As part of the interpretation, the mandatory legal requirements that apply to the recognition of partial retirement under social insurance law must therefore be taken into account. This applies to both the entitlement to a retirement pension after partial retirement (§ 237 SGB VI) and the consideration of the additional benefits provided by the employer in accordance with § 3 para. 1 No. 1 letter b AltTZG contributions to be paid for pension insurance. Partial retirement in the sense of AltTZG only applies if the employee reduces his working hours to half of the previous weekly working hours. The number of hours applicable when the partial retirement agreement is concluded is decisive for the total duration of the partial retirement. Die Vereinbarung einer variablen, von der jeweiligen tariflichen Arbeitszeit eines Vollbeschäftigten abhängigen Arbeitszeit ist ausgeschlossen. According to a decision of the Fourth Senate of February 15, 2006 (- 4 AZR 4/05 -), the provisions of a company collective agreement within the scope of the Federal Collective Bargaining Agreement for the Chemical Industry (BEntgTV) are not to the detriment of an employee who was already in force before the company collective agreement came into force Part-time retirement employment that has been completed and begun has been intervened. These results in the tariff interpretation. Nach § 3 Haustarifvertrag soll eine Tariferhöhung nach dem Verbandsta- rifvertrag für das Jahr 2003 durch eine Ausgleichszahlung abgegolten und für die Zeit ab dem 1. Juni 2004 nur zu fünfzig Prozent weitergegeben werden. Diese Regelung erfasst jedoch nicht Arbeitnehmer, die bei Inkrafttreten der Regelung bereits in einem Altersteilzeitarbeitsverhältnis standen. Bereits nach seinem Wortlaut handelt es sich bei dem Haustarifvertrag um eine Regelung im Rahmen der Tariföffnungsklauseln nach § 10 BEntgTV. Zu dieser ist eine Protokollnotiz vereinbart worden, nach der ”die Anwendung der Tariföffnungsklausel nicht in bestehende Altersteilzeitarbeitsverhältnisse eingreifen” darf. The result of the interpretation is also in accordance with the recognizable meaning and purpose of the company collective agreement. This contains a coordinated concept to ensure competitiveness and employment. It is readily understandable that these regulations are not intended to interfere with existing part-time retirement employment relationships that already make a contribution to securing employment.