MONTH:(do%,year%)
local sj%,m%(12),d%,month%
rem schaltjahr?
sj%=year%-1980
sj%=-((int(sj%/4)*4-sj%)=0)
m%(1)=31:m%(2)=28+sj% :m%(3)=31:m%(4)=30:m%(5)=31:m%(6)=30:m%(7)=31:m%(8)=31:m%(9)=30:m%(10)=31:m%(11)=30:m%(12)=31
month%=1:d%=do%+1
while (month%<13)and(d%>m%(month%))
d%=d%-m%(month%)
month%=month%+1
endwh
return month%+d%/100.0