Here’s the “sum of functions” with `ApproxFun`

:

```
julia> import ApproxFun
julia> const R = ApproxFun.Line()
ℝ
julia> f = ApproxFun.Fun(x -> x, R)
┌ Warning: Maximum number of coefficients 1048577 reached in constructing Fun.
└ @ ApproxFunBase ~/.julia/packages/ApproxFunBase/Ak6LI/src/constructors.jl:138
Fun(Chebyshev(ℝ),[0.0, 4.1937830580858183e6, 0.0, 4.193779058085821e6, 0.0, 4.193775058085823e6, 0.0, 4.193771058085826e6, 0.0, 4.1937670580858313e6 … 0.0, 17.99671143171054, 0.0, 13.997442224683063, 0.0, 9.998173017662317, 0.0, 5.998903810632585, 0.0, 1.9996346035238175])
julia> g = ApproxFun.Fun(x -> 2x, R)
┌ Warning: Maximum number of coefficients 1048577 reached in constructing Fun.
└ @ ApproxFunBase ~/.julia/packages/ApproxFunBase/Ak6LI/src/constructors.jl:138
Fun(Chebyshev(ℝ),[0.0, 8.387566116171637e6, 0.0, 8.387558116171642e6, 0.0, 8.387550116171646e6, 0.0, 8.387542116171652e6, 0.0, 8.387534116171663e6 … 0.0, 35.99342286342108, 0.0, 27.994884449366126, 0.0, 19.996346035324635, 0.0, 11.99780762126517, 0.0, 3.999269207047635])
julia> f(10)
10.572136107429396
julia> g(10)
21.14427221485879
julia> f + g
Fun(Chebyshev(ℝ),[0.0, 1.2581349174257455e7, 0.0, 1.2581337174257463e7, 0.0, 1.2581325174257468e7, 0.0, 1.258131317425748e7, 0.0, 1.2581301174257495e7 … 0.0, 53.990134295131625, 0.0, 41.99232667404919, 0.0, 29.994519052986952, 0.0, 17.996711431897758, 0.0, 5.998903810571452])
julia> (f + g)(10)
31.716404220813956
```