比较对象是A1和B1=IF(OR(A1="",B1=""),"",IF(A1=B1,"T","F"))
=if(and(a1="",b1=""),"",if(a1=b1,"T","F"))二个单元格指的是A1 B1
=if(len(a1)=0 or len(b1)=0,"",if(a1=b1,"T","F"))
=IF(AND(A1<>"",B1<>""),"",IF(A1<>B1,"F","T"))