ERROR check if a date set entered violates a previously entered date set

I am devloping an Excel program that has a list of date sets, not
necessarily in sequencial order. What I want is an ERROR CHECK if a
date set violates any date set previously entered.
What I was looking for was that a date set could not be typed in as
follows:
1/10/04 to 4/20/04
2/10/04 to 3/20/04
The second date set falls within the first set and should be invalid
setting off a message or an alert of an invalid entry. I am
interested in making it idiot proof so that one could not enter date
sets within or covering dates sets already entered. This one really
throws me, Please help.

Buzz, Are you considered to be an impatient person?

--
Don Guillett
SalesAid Software

"buzz" wrote in message
om...
I am devloping an Excel program that has a list of date sets, not
necessarily in sequencial order. What I want is an ERROR CHECK if a
date set violates any date set previously entered.
What I was looking for was that a date set could not be typed in as
follows:
1/10/04 to 4/20/04
2/10/04 to 3/20/04
The second date set falls within the first set and should be invalid
setting off a message or an alert of an invalid entry. I am
interested in making it idiot proof so that one could not enter date
sets within or covering dates sets already entered. This one really
throws me, Please help.