I just found that a behavior in importing from latex is not expected.
(define from "latex-snippet") (define to "texmacs-stree") (convert "$a b$" "latex-snippet" "texmacs-stree")
The code means that importing math formula
$a b$ from latex to texmacs. The result has an extra
* in between. The result is
(math "a*b"), what I really want is
(math "a b"). Anyone knows how to change this behavior?