We also looked at ways to make it quick to edit existing drawings, including a pen stroke that would automatically switch between inking and erasing if you move the pen backward along an existing stroke. We quickly decided that this was the more important kind of manipulation to explore — the other kind of manipulation felt like a (“small”) matter of UI design and engineering, whereas this sort of dynamic manipulation felt like a crucial part of the relationship between ink and programming. We also decided that we were confident that good-feeling deformable ink manipulation was possible, so that we could proceed with our design process assuming its existence, but that doing the work to build an ink deformation system should be deferred until later.