Just to confirm: it’s 1/(1-x) and not 1/(1-t), correct? So that the term can be pulled out? I think this works:
d = Segment(0.5,0)
x = Fun(d)
V = Volterra(Legendre(d))
u = (I - 1/(1-x) * V) \ 1
If you meant 1/(1-t) just put it to the right of the V, (using a bracket so it knows you don’t want to apply the operator to the function 1/(1-x)):
u = (I - V[1/(1-x)]) \ 1