Puzzle #15

The inhabitants of mars use the same mathematical operations that we do, namely + -

They also use the operator ☻ that we do not know.

The following are true for any REAL numbers x and y:

x☻0 = x

x☻y = y☻x

(x+1)☻y = (x☻y)+y+1

 

What is the value of 12☻5?