From: Rabbi Akiva Eiger
To: Unknown recipient
This is a letter from Rabbi Shlomo Eiger to his father Rabbi Akiva Eiger, addressing a difficulty in Tosfos regarding why a special verse is needed to prohibit a blemished animal for altar use. Rabbi Shlomo Eiger offers three analytical approaches, with his primary innovation being that every issur mosif inherently carries an element of stringency relative to the prohibition it expands upon; he ultimately maintains that this middle approach remains viable even after acknowledging weaknesses in the other two.
Source: Shu"t Rabbi Akiva Eiger §170