calc-embedded-open-formula

calc-embedded-open-formula is a variable defined in `calc.el'.
Its value is

"\\`\\|^\n\\|\\$\\$?\\|\\\\\\[\\|^\\\\begin[^{].*\n\\|^\\\\begin{.*[^x]}.*\n\\|^@.*\n\\|^\\.EQ.*\n\\|\\\\(\\|^%\n\\|^\\.\\\\\"\n"

Documentation:
A regular expression for the opening delimiter of a formula used by calc-embedded.

You can customize this variable.