[undelete].
'Command examples:       CHECK|: undelete [3,5,6].'.
'                        CHECK|: undelete h#3 & h#5-6.'.
''.
'The "undelete" command allows you to tell the checker to undelete one or'.
'more deleted hypotheses of the current VC, so that these hypotheses will'.
'once again be useable by the checker in proof steps'.
