\xtwoheadleftarrow{abc}The command \xtwoheadleftarrow{abc} is used to create an extensible arrow symbol that points to the left with two heads, and it can be customized with the label 'abc' above the arrow. This is typically used in mathematical contexts where a specific type of mapping or transformation is denoted by a double-headed arrow, often indicating a surjective function or a specific type of relation.
Indicates a surjective function f from set B to set A.
A \xtwoheadleftarrow{f} BRepresents a transformation or mapping labeled by alpha from Y to X.
X \xtwoheadleftarrow{\alpha} YDenotes a projection mapping pi from N to M.
M \xtwoheadleftarrow{\pi} N