Any Possibility Of Creating A MUTUALLY Dependent CHECK

Hi,

DDL:
-- create table #task (taskID int identity(1,1) primary key, taskName
varchar(25) unique, taskCompleteDate dateTime, taskComplete bit
default(0));
/*
Business Rules:
a) if taskCompleteDate is NULL (like default) then, taskComplete may
not be set to 1 (attempt to update it to 1 would fail);
b) else automatically set taskComplete = 1
*/
I was thinking using CHECK constraint (mutual constraint if possible),
along the following line:
CHECK (if taskCompleteDate is null set taskComplete=0 else set
taskComplete=1)

Hmm, your thought?
Thanks.