Now substituting: ∫ ∫ p ( t ) ¯ ¯ ⋅ ⋅ e A t d t | t = z = Q z , ∫ ∫ p ( t ) ¯ ¯ ⋅ ⋅ e B t d t | t = z = R z ,where ∫ ∫ x ( t ) d t | t = z is the primitive of x (t) computed at t = z, in the case z = t this integral is the primitive itself, yields: