  We perform both distorted black hole evolutions and binary black hole head on
collisions and compare the results of using a full grid to results obtained by
excising the black hole interiors. In both cases the evolutions are found to
run essentially indefinitely, and produce the same, convergent waveforms.
Further, since both the distorted black holes and the head-on collision of
puncture initial data can be carried out without excision, they provide an
excellent dynamical test-bed for excision codes. This provides a strong
numerical demonstration of the validity of the excision idea, namely the event
horizon can be made to "protect" the spacetime from the excision boundary and
allow an accurate exterior evolution.

General Relativity and Quantum Cosmology