singletons de elements de conjunts

z€{x} <==> z = x
z€}x{ <==> ¬( z = x )


1 = {0}
(-1) = }0{


z€{x,y} <==> ( z = x or z = y )
z€}x,y{ <==> ( ¬( z = x ) & ¬( z = y ) )


2 = {0,{0}}
(-2) = }0,{0}{


{x} [<< {x,y}
}x{ >>] }x,y{


{x} [W] {y} = {x,y}
}x{ [M] }y{ = }x,y{


[M]{x,y} = x [M] y <==> (  t€[M]{x,y} <==> [Az][ z€{x,y} ==> t€z ] )
[W]{x,y} = x [W] y <==> (  t€[W]{x,y} <==> [Ez][ z€{x,y} & t€z ] )


[M]}x,y{ = ¬( x [W] y ) = ( ¬x [M] ¬y ) <==> (  t€[M]}x,y{ <==> [Az][ z€}x,y{ ==> t€z ] )
[W]}x,y{ = ¬( x [M] y ) = ( ¬x [W] ¬y ) <==> (  t€[W]}x,y{ <==> [Ez][ z€}x,y{ & t€z ] )