- | {node=node;son=son;brother=brother} when
- is_symbol_dummy node &&
- is_tree_dummy son &&
- is_tree_dummy brother -> DeadEnd
- | x -> Node x
+ | {node=node;son=son;brother=brother} ->
+ let bn = is_symbol_dummy node in
+ let bs = is_tree_dummy son in
+ let bb = is_tree_dummy brother in
+ let son = if bs then DeadEnd else son in
+ let brother = if bb then DeadEnd else brother in
+ if bb && bs && bn then
+ DeadEnd
+ else
+ if bn then
+ Node {node=Sself;son=son;brother=brother}
+ else
+ Node {node=node;son=son;brother=brother}