#### Vertical Compositions

The `cvert` function makes a vertical composition. Each component of the vector is centered in a column. The baseline of the result is by default the top line of the resulting composition. For example, `f(cvert([a, bb, ccc]), cvert([a^2 + 1, b^2]))' formats in Big mode as

```f( a ,  2    )
bb   a  + 1
ccc     2
b
```

There are several special composition functions that work only as components of a vertical composition. The `cbase` function controls the baseline of the vertical composition; the baseline will be the same as the baseline of whatever component is enclosed in `cbase`. Thus `f(cvert([a, cbase(bb), ccc]), cvert([a^2 + 1, cbase(b^2)]))' displays as

```        2
a  + 1
a      2
f(bb ,   b   )
ccc
```

There are also `ctbase` and `cbbase` functions which make the baseline of the vertical composition equal to the top or bottom line (rather than the baseline) of that component. Thus `cvert([cbase(a / b)]) + cvert([ctbase(a / b)]) + cvert([cbbase(a / b)])' gives

```        a
a       -
- + a + b
b   -
b
```

There should be only one `cbase`, `ctbase`, or `cbbase` function in a given vertical composition. These functions can also be written with no arguments: `ctbase()' is a zero-height object which means the baseline is the top line of the following item, and `cbbase()' means the baseline is the bottom line of the preceding item.

The `crule` function builds a "rule," or horizontal line, across a vertical composition. By itself `crule()' uses `-' characters to build the rule. You can specify any other character, e.g., `crule("=")'. The argument must be a character code or vector of exactly one character code. It is repeated to match the width of the widest item in the stack. For example, a quotient with a thick line is `cvert([a + 1, cbase(crule("=")), b^2])':

```a + 1
=====
2
b
```

Finally, the functions `clvert` and `crvert` act exactly like `cvert` except that the items are left- or right-justified in the stack. Thus `clvert([a, bb, ccc]) + crvert([a, bb, ccc])' gives:

```a   +   a
bb     bb
ccc   ccc
```

Like `choriz`, the vertical compositions accept a second argument which gives the precedence to use when formatting the components. Vertical compositions do not support separator strings.