The lift command folds away part of the proof tree. It is useful when the tree has become illegible due to the scale factor needed to make the tree fit in the window, and is useful on subtrees whose proof has been completed, to speed up the drawing of the tree. It is applicable to internal nodes of the tree. If the inspected node is the only selection, then the entire subtree rooted at that node is folded away, except for any unproven leaf nodes in that subtree: the unproven leaf nodes are lifted up to the inspected node. If instead there are some crossed nodes, then the subtrees rooted at those crossed nodes are lifted up to the inspected node, folding away everything in between. The crossed nodes must be descendants of the inspected node.