u = - f
The symbol - is used as notation for the negation of Lie homomorphisms.
i1 : M = lieAlgebra{a,b} o1 = M o1 : LieAlgebra
i2 : L = lieAlgebra{a,b} o2 = L o2 : LieAlgebra
i3 : f = map(L,M) o3 = f o3 : LieAlgebraMap
i4 : describe(-f) o4 = a => - a b => - b source => M target => L