Essential welded pairs: S: U = 1 2 3 4 1 2 3 4 1 4 2 3 1 3 4 2 D = 1 2 3 4 1 2 4 3 1 2 4 3 1 2 4 3 T: U = 1 2 3 4 1 2 4 3 1 2 4 3 1 2 4 3 D = 1 2 3 4 1 2 4 3 1 2 4 3 1 2 4 3 S: U = 1 2 3 4 1 2 4 3 4 2 1 3 3 2 4 1 D = 1 2 4 3 1 2 4 3 1 2 4 3 1 2 4 3 T: U = 1 2 4 3 1 2 4 3 1 2 4 3 1 2 4 3 D = 1 2 4 3 1 2 4 3 1 2 4 3 1 2 4 3 S: U = 1 2 3 4 3 4 1 2 4 3 2 1 2 1 4 3 D = 1 4 2 3 1 4 2 3 1 4 2 3 1 4 2 3 T: U = 1 3 4 2 1 3 4 2 1 3 4 2 1 3 4 2 D = 1 4 2 3 1 4 2 3 1 4 2 3 1 4 2 3 S: U = 1 2 3 4 1 2 4 3 1 2 3 4 1 2 3 4 D = 1 2 4 3 1 2 4 3 4 2 3 1 3 2 1 4 T: U = 1 2 4 3 1 2 4 3 1 2 4 3 1 2 4 3 D = 1 2 4 3 1 2 4 3 1 2 4 3 1 2 4 3 S: U = 1 3 4 2 1 3 2 4 1 2 4 3 1 4 3 2 D = 1 4 2 3 1 3 4 2 1 3 4 2 1 3 4 2 T: U = 1 3 4 2 1 4 2 3 1 4 2 3 1 4 2 3 D = 1 4 2 3 1 3 4 2 1 3 4 2 1 3 4 2 S: U = 2 1 4 3 2 1 4 3 2 1 4 3 2 1 4 3 D = 3 1 4 2 2 4 1 3 2 4 1 3 3 1 4 2 T: U = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 D = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 S: U = 1 4 2 3 3 2 4 1 4 1 3 2 2 3 1 4 D = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 T: U = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 D = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 S: U = 1 4 3 2 4 2 3 1 1 2 3 4 2 1 3 4 D = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 T: U = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 D = 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4