How is this past tense??
The infix ja indicates the immediate past in the negative tense, i.e. corresponding to me in a positive sentence:
Kitabu kimepotea: the book is lost.
Kitabu hakijapotea: the book is not lost.
Hope that helps.
So this should be: "the book WAS not lost!"
That would be 'Kitabu hakikupotea'
The Prefix of ki/vi- Ngeli is haki- (sgl. ) and havi-(pl.). The correct form would be :
haki-KU-potea for both present perfect and past tense. Haki-JA-potea means:
The book is NOT YET lost.