A question about Feynman's book of Path. integrals

[aife]

Page 35 Feynman Quantum Mechanics and Path Integrals
(2-26)ψ=(iε)^R

I know it's a defination.But how to find some threads.How can we get this?

 

[USeptim]

Hello aife, maybe you have to give some more information about the matter, otherwise those who don't have the book won't be able to help you.Sergio

 

[aife]

Thanks for your advice.
Here's the quote: