diffLie -- the derivation obtained from the differential defined in the current Lie algebra

i1 : L=lieAlgebra({a,b,c},{[a,a,b],[a,c]},
         genWeights=>{{1,0},{1,0},{2,1}},genDiffs=>{[],[],[a,b]},genSigns=>1)

o1 = L

o1 : LieAlgebra

i2 : diffLie()

o2 = DerLie{...8...}

o2 : DerLie

i3 : peek oo

o3 = DerLie{a => []                  }
            b => []
            c => [a, b]
            maplie => MapLie{...5...}
            signDer => 1
            sourceLie => L
            targetLie => L
            weightDer => {0, -1}