use the mul command

mul([a,b,c,d,1])= a*b*c*d

Hey,

it seems to me like the multiplication operator between b and (1+x/l) is missing. Maple thinks that you set the funktion b(g(x,l))=1 whereas g=1/(1+x/l). This works:

Hope that helped!

Hey,

looks like you have the same problem as I had:
http://www.mapleprimes.com/questions/209502-Problem-With-Substitution

the solution is to convert to D and substitute there. You might also want to use freeze and thaw.

this will do the trick:

q1 := b(t)*(diff(c(t), t))*(diff(a(t), t))+a(t)*(diff(b(t), t))

subs(b(t)=0,convert(q1,D))

q1:=convert(%,diff)

Hope this helps!