Majority function: An LED is lit $($f$=1)$ if any three or all four of the switches $($represented by $0000$

Boolean variables a$,$ b$,$ c$,$ d$)$ are in the same position, where $1$ represents the ON position of a $0001$

switch, and $0$ the OFF position.

The Boolean variable f is represented by an LED $(1$: LED is ON$,0$: LED is OFF$).$ For example: if abcd$=1010->-$ f$=0.$ If abcd$=0010->$ f$=1$