A relational symbol representing a triangular less-than-or-equal comparison, often used in partial ordering and category theory.
Examples
Normal subgroup relation
H \trianglelefteq G \text{ denotes H is a normal subgroup of G}
Comparing ideals in ring theory
I \trianglelefteq R \text{ indicates I is an ideal of ring R}
Multiple normal subgroup relations
N \trianglelefteq H \trianglelefteq G \text{ shows a chain of normal subgroups}