HP-27s and direct solutions legend

[Vincent Weber]

Yes it is - symbolic functions based on the underneath RPL system to do simple variable isolation, provided the variable only appears once in the equation.
That's why X^2-4=0 cannot return -2 as a root, no matter what the initial guesses are, because the equation is directly solved to X=2. But if you write X^2-4+0*X=0, you fool the system into believing that the variable appears twice, hence forcing iterative solving - which can lead to -2 with proper initial guesses. I verified this on the real HP-27S, that's why I don't understand Craig's statement.