Not
  

Returns reversed logical value.

syntax
Not(number)

input
logical value: 1 or 0 (True or False).

returns
1(True) when number is 0
0(False) when number is 1 1(Fałsz).

example
Not(1) = 0
Not(0) = 1
Not(2>1) = 0
Not(2<=1) = 1
If(Not(2<=1);10;20) = 10