%mode init
B1=NA()
B2=B1
B3=ISNA(B1)
B4=ISNA(B2)
B5=ISNA(B3)
B6=ISNA(1)
B7=ISNA("str")
B8=ISNA(NA())
%calc
%mode result
B1=#N/A
B2=#N/A
B3=true
B4=true
B5=false
B6=false
B7=false
B8=true
%check