This probably is a rudimentary question. I would like to have a simple analog (switch) circuit for addition modular 2, or \$a_1+a_2+\cdots +a_n \$ (mod 2). Certainly, digital transistors can accomplish this, but I would prefer analog devices if the circuit is simpler. In practical terms, I would like to design a switch circuit to control a light, where fixing all other switches, any one of them can switch the light on and off. For \$n=2\$ or 2 switches, someone earlier has already suggested using two back to back single-pole-double-throw switches.
For 4 places see below: -
For 3 places remove one of the two pole switches. For more than 4 just keep repeating the 2 pole switches.