  In the same way the folding of the Dynkin diagram of A_{2n} (resp. A_{2n-1})
produces the B_n (resp. C_n) Dynkin diagram, the symmetry algebra W of a Toda
model based on B_n (resp. C_n) can be seen as resulting from the folding of a
W-algebra based on A_{2n} (resp. A_{2n-1}). More generally, W algebras related
to the B-C-D algebra series can appear from W algebras related to the unitary
ones. Such an approach is in particular well adapted to obtain fusion rules of
W algebras based on non simply laced algebras from fusion rules corresponding
to the A_n case. Anagously, super W algebras associated to orthosymplectic
superalgebras are deduced from those relative to the unitary A(m,n) series.
