[standardise].
'Command examples:       CHECK|: standardise.'.
'                        CHECK|: standardise i-1+1.'.
'                        CHECK|: standardise p or not p.'.
'                        CHECK|: standardise h#7.'.
'                        CHECK|: standardise c#3.'.
''.
'This command may be used to convert a current hypothesis or conclusion'.
'into standard form, or to standardise a user-supplied expression.'.
'Once calculated, the standardised expression is displayed, and the'.
'user has the choice of whether or not the new expression should be'.
'saved.  If the user opts to save the standardised expression, it either'.
'overwrites the old expression (if a hypothesis or conclusion is given)'.
'or it is added as a new hypothesis, e.g. saving the fact that i-1+1 has'.
'the standard form i results in the addition of a new hypothesis i-1+1=i.'.
'If a user-supplied boolean expression was given, the result will'.
'be saved either by saving the original expression (if the standard form'.
'is "true") or by adding the new hypothesis OLD_EXPR <-> NEW_EXPR.'.
