I have questions about chapters 5 & 9 in Srednicki's book. 1. Below eq. (5.18), he says "$<p|\phi (0)|0>$ is a Lorentz-invariant number.", but I do not know why. 2. Below eq. (5.26), he says "After shifting and rescailing (and renaming some parameters)". Are $m$ and $g$ in eq. (5.26) different from ones in eq. (5.27)? 3. Below eq. (9.9), he says "as we will see, "$Y=O(g)$ and $Z_i =1+O(g^2)$", which means these g-dependence is just the expectation at this stage. In eq. (9.18), however, he used $Z_g =1+O(g^2)$ without showing this $Z_g$-behavior. Is my understanding incorrect?