Doubt in the 7 - Gridap Darcy Equation Tutorial

Hi everyone,

I’m new on Julia and I have two doubts about how Julian works:

In this tutorial a function is defined to define differents properties in different parts of the domain:

function σ(x,u)
if ((abs(x[1]-0.5) <= 0.1) && (abs(x[2]-0.5) <= 0.1))
return kinv2⋅u
else
return kinv1⋅u
end
end

I don’t understand why then in the bilinear form the following composition is needed to use this function:
σ∘(px,u)
What sense have this composing?

Could you link the tutorial?