isIrreducible -- Whether a Lie algebra module is irreducible or not

i1 : g=simpleLieAlgebra("A",2)

o1 = g

o1 : simple LieAlgebra

i2 : M=irreducibleLieAlgebraModule({2,1},g)

o2 = M

o2 : irreducible LieAlgebraModule over g

i3 : isIrreducible M

o3 = true

i4 : isIrreducible(M++M)

o4 = false

i5 : isIrreducible(M**M)

o5 = false