\ntriangleleft
The symbol \ntriangleleft is used to denote that one element is not a normal subgroup of another in group theory. It is the negation of the \triangleleft symbol, which indicates a normal subgroup relation.
H is not a normal subgroup of G
H \ntriangleleft G
K is not a normal subgroup of L
K \ntriangleleft L
N is not a normal subgroup of M
N \ntriangleleft M