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### 4.2 Help Commands

The `?` key (`calc-help`) displays a series of brief help messages. Some keys (such as `b` and `d`) are prefix keys, like Emacs' <ESC> and `C-x` prefixes. You can type `?` after a prefix to see a list of commands beginning with that prefix. (If the message includes ‘`[MORE]`’, press `?` again to see additional commands for that prefix.)

The `h h` (`calc-full-help`) command displays all the `?` responses at once. When printed, this makes a nice, compact (three pages) summary of Calc keystrokes.

In general, the `h` key prefix introduces various commands that provide help within Calc. Many of the `h` key functions are Calc-specific analogues to the `C-h` functions for Emacs help.

The `h i` (`calc-info`) command runs the Emacs Info system to read this manual on-line. This is basically the same as typing `C-h i` (the regular way to run the Info system), then, if Info is not already in the Calc manual, selecting the beginning of the manual. The `C-x * i` command is another way to read the Calc manual; it is different from `h i` in that it works any time, not just inside Calc. The plain `i` key is also equivalent to `h i`, though this key is obsolete and may be replaced with a different command in a future version of Calc.

The `h t` (`calc-tutorial`) command runs the Info system on the Tutorial section of the Calc manual. It is like `h i`, except that it selects the starting node of the tutorial rather than the beginning of the whole manual. (It actually selects the node “Interactive Tutorial” which tells a few things about using the Info system before going on to the actual tutorial.) The `C-x * t` key is equivalent to `h t` (but it works at all times).

The `h s` (`calc-info-summary`) command runs the Info system on the Summary node of the Calc manual. See Summary. The `C-x * s` key is equivalent to `h s`.

The `h k` (`calc-describe-key`) command looks up a key sequence in the Calc manual. For example, `h k H a S` looks up the documentation on the `H a S` (`calc-solve-for`) command. This works by looking up the textual description of the key(s) in the Key Index of the manual, then jumping to the node indicated by the index.

Most Calc commands do not have traditional Emacs documentation strings, since the `h k` command is both more convenient and more instructive. This means the regular Emacs `C-h k` (`describe-key`) command will not be useful for Calc keystrokes.

The `h c` (`calc-describe-key-briefly`) command reads a key sequence and displays a brief one-line description of it at the bottom of the screen. It looks for the key sequence in the Summary node of the Calc manual; if it doesn't find the sequence there, it acts just like its regular Emacs counterpart `C-h c` (`describe-key-briefly`). For example, `h c H a S` gives the description:

         H a S runs calc-solve-for:  a `H a S' v  => fsolve(a,v)  (?=notes)

which means the command `H a S` or `H M-x calc-solve-for` takes a value ‘`a`’ from the stack, prompts for a value ‘`v`’, then applies the algebraic function `fsolve` to these values. The ‘`?=notes`’ message means you can now type `?` to see additional notes from the summary that apply to this command.

The `h f` (`calc-describe-function`) command looks up an algebraic function or a command name in the Calc manual. Enter an algebraic function name to look up that function in the Function Index or enter a command name beginning with ‘`calc-`’ to look it up in the Command Index. This command will also look up operator symbols that can appear in algebraic formulas, like ‘`%`’ and ‘`=>`’.

The `h v` (`calc-describe-variable`) command looks up a variable in the Calc manual. Enter a variable name like `pi` or `PlotRejects`.

The `h b` (`calc-describe-bindings`) command is just like `C-h b`, except that only local (Calc-related) key bindings are listed.

The `h n` or `h C-n` (`calc-view-news`) command displays the “news” or change history of Calc. This is kept in the file `README`, which Calc looks for in the same directory as the Calc source files.

The `h C-c`, `h C-d`, and `h C-w` keys display copying, distribution, and warranty information about Calc. These work by pulling up the appropriate parts of the “Copying” or “Reporting Bugs” sections of the manual.