>>172
ψ(x) = ∫[ {1/(p^2 + a^2)} * exp(ipx) ] dp
=2πiRes(Im p>0)({1/(p^2 + a^2)} * exp(ipx))
=2πiRes(Im p>0)(1/(2ai)*(1/(p-ai)-1/(p+ai))*exp(ipx))
=2πi[1/(2ai)*(exp(-ax))]
=π/a*exp(-ap)