@echo off & setlocal
for /f "delims==" %%a in ('set BASIC_ID[ 2^>nul') do set "%%a="
for /f "usebackq tokens=*" %%a in ("1.txt") do set "BASIC_ID[%%a]=True"
for /f "usebackq tokens=*" %%a in ("2.txt") do if not defined BASIC_ID[%%a] echo;%%a
endlocal