I'm currently using Math Time Pro2, but considering the
\exists is not suitable for my liking. How can I change back to the origin LaTeX
One more question, is that is there a more-straight (double) (left) right arrow? (I mean, in the "head" of the arrow) The
\rightarrow-like symbol all have curly embellishment, which I don't want.
You can load a math symbol font:
Look at the comparison and decide whether you really want the change.