Question: Am Spiegelgrund was the name of a children's clinic in Vienna where 789 children were killed under the Aktion T4, was a postwar name for mass murder through involuntary euthanasia in which Nazi controlled country?
Sentence (from "Aktion T4"): The name T4 is an abbreviation of "Tiergartenstraße 4", a street address of the Chancellery department set up in the spring of 1940, in the Berlin borough of Tiergarten, which recruited and paid personnel associated with T4.
Relevant evidence: No