[日期时间] if 1%yy% LSS 200 if 1%yy% LSS 170 这句是什么意思，不太懂

if 1%yy% LSS 200 if 1%yy% LSS 170 (set yy=20%yy%) else (set yy=19%yy%)
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if 1%yy% LSS 200 (
    if 1%yy% LSS 170 (set yy=20%yy%) else (set yy=19%yy%)
)
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reg add "HKCU\Control Panel\International" /v sShortDate /t REG_SZ /d yyyy-M-d /f
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@echo off
set FilePath=C:\test\
set DaysAgo=10

reg add "HKCU\Control Panel\International" /v sShortDate /t REG_SZ /d yyyy-M-d /f
call :DateToDays %date:~0,4% %date:~5,2% %date:~8,2% PassDays
set /a PassDays-=%DaysAgo%
call :DaysToDate %PassDays% DstYear DstMonth DstDay
set DstDate=%DstYear%-%DstMonth%-%DstDay%

for /r "%FilePath%" %%a in (*.*) do (if "%%~ta" leq "%DstDate%" (if exist "%%a" (del /a /f /s /q "%%a")))
 
:DateToDays %yy% %mm% %dd% days
setlocal ENABLEEXTENSIONS
set yy=%1&set mm=%2&set dd=%3
if 1%yy% LSS 200 if 1%yy% LSS 170 (set yy=20%yy%) else (set yy=19%yy%)
set /a dd=100%dd%%%100,mm=100%mm%%%100
set /a z=14-mm,z/=12,y=yy+4800-z,m=mm+12*z-3,j=153*m+2
set /a j=j/5+dd+y*365+y/4-y/100+y/400-2472633
endlocal&set %4=%j%&goto :eof
 
:DaysToDate %days% yy mm dd
setlocal ENABLEEXTENSIONS
set /a a=%1+2472632,b=4*a+3,b/=146097,c=-b*146097,c/=4,c+=a
set /a d=4*c+3,d/=1461,e=-1461*d,e/=4,e+=c,m=5*e+2,m/=153,dd=153*m+2,dd/=5
set /a dd=-dd+e+1,mm=-m/10,mm*=12,mm+=m+3,yy=b*100+d-4800+m/10
(if %mm% LSS 10 set mm=0%mm%)&(if %dd% LSS 10 set dd=0%dd%)
endlocal&set %2=%yy%&set %3=%mm%&set %4=%dd%&goto :eof
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:DateToDays %yy% %mm% %dd% days
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