Constructor throws exception if given atom is null. Only
AtomLink.Tab instances can have a null atom field.
public java.lang.String toString()
toString in class java.lang.Object
public void remove()
Disconnects this linker from the linkers above and below it, and
puts them in sequence, repairing the hole. There is no indication
in the linker itself that it is no longer part of the tree (unless
Debug is on).