 If "M" has a normal form, the Böhm tree is finite and has a simple correspondence to the normal form.If "M" does not have a normal form, the procedure may "grow" some subtrees infinitely, or it may get "stuck in a loop" attempting to produce a result for part of the tree, which is the source of unlabeled leaf nodes.For this reason the procedure should be understood as applying all steps in parallel, with the resulting tree given "in the limit" of applying the procedure infinitely.