Caretaker class

Sometimes it is necessary to perform undo multiple steps. In this case, create a Caretaker class that holds a stack of Memento objects. If redo is desired, then have two stacks in the Caretaker, one for undo and one for redo, and the Memento object that is popped from the undo stack gets pushed into the redo stack and vice versa. The code example is as follows ... 

There are two classes of tumour suppressor genes gatekeeper genes and caretaker genes. If the activity of a... 

Genes and proteins known as caretakers have an indirect influence on tumor formation. These are susceptibility genes that indirectly suppress tumor formation. An important class of caretakers includes repair proteins. Inactivation of a caretaker gene of this class leads to a sharp increase in mutation rate and is therefore equivalent to constant exposure to mutagens. 

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