Please use valid matlab syntax for your example so we don't have to wonder what your inputs actually are. A={(1,2,3),(1,2,4),(1,3,5),(1,2,6)} is not valid matlab, so we don't know how your sets are stored.
I'm going to assume that they're stored as rows of a matrix as that's the simplest:
A = [1 2 3; 1 2 4; 1 3 5; 1 2 6];
B = [1 2 6; 1 2 4];
setdiff(A, B, 'rows') %simple!
