Horizontal Compositions
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The `choriz' function takes a vector of objects and composes
them horizontally.  For example, `choriz([17, a b/c, d])' formats
as `17a b / cd' in normal language mode, or as

       a b
     17--d
        c

in Big language mode.  This is actually one case of the general
function `choriz(VEC, SEP, PREC)', where either or both of SEP and
PREC may be omitted.  PREC gives the "precedence" to use when
formatting each of the components of VEC.  The default precedence is
the precedence from the surrounding environment.

SEP is a string (i.e., a vector of character codes as might be entered
with `" "' notation) which should separate components of the
composition.  Also, if SEP is given, the line breaker will allow lines
to be broken after each occurrence of SEP.  If SEP is omitted, the
composition will not be breakable (unless any of its component
compositions are breakable).

For example, `2 choriz([a, b c, d = e], " + ", 180)' is formatted as
`2 a + b c + (d = e)'.  To get the `choriz' to have precedence 180
"outwards" as well as "inwards," enclose it in a `cprec' form: `2
cprec(choriz(...), 180)' formats as `2 (a + b c + (d = e))'.

The baseline of a horizontal composition is the same as the baselines
of the component compositions, which are all aligned.