LaTeX for Logicians

proof.sty: A User Guide

4. Further tricks and tips

a To centre proofs with spacing above and below, place in a standard mathmode context '$$ .... $$'. More than one proof in the same context will be set with their conclusions aligned: the proofs can be spaced using e.g. '\quad'. For example:

$$
\infer[(\to I)]
     {(A \to B)}
     {
     \infer*{B}{[A]}
     }
\qquad
\infer[(\to E)]
     {B}
     {(A \to B) & A}
$$

b If a proof is set in-line, then its conclusion sits on the current line and the rest of the proof is above the line. To centre a proof vertically, you can use the TeX command '\vcenter'. For instance ...

The rule 
$\vcenter
{
\infer
    {(A \to B)}
    {
    \infer*{B}{[A]}
    }
}$
is known as $\to$-introduction

c Other TeX commands (particularly '\kern') can be used for horizontal fine-tuning. Interline vertical spacing within a proof is controlled by the dimension 'inferLineSkip' whose default value is 2 pt. To increase this you can prefix your proof with e.g. '\inferLineSkip=4pt'.