Parses the given string into a TeXFormula, puts it in the upper
left corner over a root sign (nthRoot), puts the current TeXFormula under this
root sign and changes the current TeXFormula into this resulting root construction.
Puts the given TeXFormula in the upper left corner over a root sign, puts the
current TeXFormula under this root sign and changes the current TeXFormula
into this resulting root construction.