If someone does not purchase a seat at a synagogue for high holidays and does not ask the synagogue for permission to pray there, is it forbidden to walk in and sit in the vacant seat of a no-show or stand in standing room in order to be present at any part of the service? Is it forbidden to be present during a shofar blowing in order to fulfill the mitzvah of hearing the shofar or recite Yizkor on Yom Kippur or to fulfill any other mitzvah? Is this considering stealing from the congregation?