what are the weakest preconditions of these following statements what is the meaning of postcondition and weakest postcondition in terms of programing and what are weakest postconditons of following statements.
1. a=2*(b-1)-1   {a&gt;0}
2. b=(c+10)/3    {b&gt;6}
3. a=(a+2*b-1)   {a&gt;1}
4. a=2*b+1;b=a-3 {b&lt;0}
Let's do the first one. You want to find what condition on $b$ will imply $2(b-1)-1&gt;0$. All you have to do is solve this inequality.
The other ones are similar.