LGTM
https://codereview.appspot.com/551820043/diff/563910043/lily/stencil-integral.cc File lily/stencil-integral.cc (left): https://codereview.appspot.com/551820043/diff/563910043/lily/stencil-integral... lily/stencil-integral.cc:854: if (not scm_is_pair (expr)) LGTM. I forgot that keyword existed! :D