multDerLie -- defines the Lie multiplication of two derivations on a Lie algebra

i1 : L=lieAlgebra({a,b},{})

o1 = L

o1 : LieAlgebra

i2 : da=derLie({[],[a,b]})

o2 = da

o2 : DerLie

i3 : db=derLie({[b,a],[]})

o3 = db

o3 : DerLie

i4 : multDerLie(da,db)

o4 = DerLie{...7...}

o4 : DerLie

i5 : peek oo

o5 = DerLie{a => [a, b, a]           }
            b => [b, b, a]
            maplie => MapLie{...4...}
            signDer => 0
            sourceLie => L
            targetLie => L
            weightDer => {2, 0}