basic doubt

[SHIKHA]

i have a basic doubt in hypothesis testing...

in a book written ..(Def.) "p value" is the lowest of significance (alpha value) at which the null can be rejected.
 
so if in an eg p value equals alpha value then we reject the null according to the definition written above..but i dnt understand why..???

becoz decision rule says in case of two tail test...the null will not be rejected if z test value lies btw + - z critical value at alpha /2 value so if p=alpha den decision rule and definition contradict..

please tell me if i am wrong...