[traverse].
'Command examples:      CHECK|: traverse.'.
'                       CHECK|: traverse h#8.'.
'                       CHECK|: traverse c#2.'.
'                       CHECK|: traverse X where h#5=(X or _).'.
''.
'This command may be used to "explore" the structure of an expression to'.
'whatever depth is required, and is particularly useful in gaining an'.
'understanding of the composition of large expressions.'.
''.
'One enters at the toplevel of the chosen expression and may descend via'.
'dN (Down argument number N) and ascend via u (up) commands.  At any'.
'level, r redisplays the principal functor (function or operator at the'.
'top of the current expression tree) and arguments, t shows typechecking'.
'information for this level, l shows the location of the current'.
'subexpression within the toplevel expression (lb - the default - is'.
'"locate brief" in which other subexpressions are abbreviated to ...,'.
'while lf - "locate full" - does not abbreviate), s shows the toplevel'.
'expression in full and h displays a help summary of traverse commands.'.
'To exit from the traverse command, type x.'.
''.
'Traverse commands may be in either upper or lower case, and do not need'.
'termination by a full-stop - though any which are typed will be ignored.'.
'Multiple commands may be typed on a line, with optional white-space'.
'separators.  Synonyms permitted are "-" for "u" (up), "+" for "d" (down)'.
'and "?" for "h" (help).'.
