Use phantom{-} in (up a b), where only one of a and b have a minus si…

…gn and the lengths are similar

racket-cas/format.rkt

@@ -107,11 +107,16 @@
   (parameterize ([output-wrapper values])
     (define x (verbose~ u))
     (define y (verbose~ v))
+    (when (and (= (string-length x) (+ (string-length y) 1))
+               (eqv? (string-ref x 0) #\-))
+      (set! y (~a "\\phantom{-}" y)))
+    (when (and (= (string-length y) (+ (string-length x) 1))
+               (eqv? (string-ref y 0) #\-))
+      (set! x (~a "\\phantom{-}" x)))    
     (if (output-brackets-for-up?)
         (~a "\\begin{bmatrix} " x "\\\\" y "\\end{bmatrix}")
         (~a "\\begin{pmatrix} " x "\\\\" y "\\end{pmatrix}"))))
 
-
 ;;; Intervals
 (define (default-output-interval u)
   (define v~ verbose~)