What is the source that R' Yehoshua's father was R' Yechiel Michel? I found in the sefer Gevuros Ha'Ari (biography of R' Aryeh Leib Epstein, Ba'al HaPardes) that he was a grandson of R' Avraham Epstein, but it doesn't say there who his father was. Any information on this would be greatly appreciated. Thank you!