On lambda calculus notation: FGa If we've got this expression:

FGa

where F and G are functions (as well as a, of course; but let's treat a as a constant).
It must be understood that:
first apply F taking G as input; then apply the previous result with a as input. This is

FGa = (FG)a

conventionally expressed:

( F(G) )( a )

Or is it this instead:

FGa == F(Ga) == F(G(a))

Thanks.
It's the first one. Function application is left-associative.
$$FGa = (F G) a$$