\twoheadleftarrowThe \twoheadleftarrow command in LaTeX is used to produce a two-headed left arrow. This type of arrow is often used in mathematical contexts to denote functions or mappings that are surjective (onto). It can also be used in various diagrammatic representations to indicate a specific type of relationship or transformation.
Denotes a surjective function from set Y to set X.
f : X \twoheadleftarrow YIndicates a sequence of surjective mappings from C to B to A.
A \twoheadleftarrow B \twoheadleftarrow CUsed in a diagram to explicitly label an arrow as representing an onto mapping.
\twoheadleftarrow_{\text{onto}}