Why super._health += 1; does not work?

[ayumilove]

super._health += 1;
super._health -= 1;
super._health *= 1;
super._health /= 1;

Syntax error: expecting semicolon before plusassign. :sen:
Syntax error: expecting semicolon before minusassign. :sen:
etc

However, this works:-

super._health = super._health + 1;