Two (supposedly) trival questions in Schwartz's QFT notes. The notes can be found here. 1. page 155, equation 15.2, how does the integrand reduce to k dk? I would guess that there must be some logarithm, but k dk? 2. page 172, equtiation 17.11, why is it legal to shift the variable that way? Will the x integral not notice when we add the x to the equation? I mean, the one x term comletlely disappears after the shifting. thank you!