Radovan Garabik wrote: > because neither in mathematics people agree on the order: > a°b(x) == a(b(x)) or > a°b(x) == b(a(x)) ? Is this a joke or what? In mathematics people DO agree on the order: if a:B->A and b:X->B, then a°b:X->A and (a°b)(x)=a(b(x))