definition g : list nat → list nat → nat
| []          (y::ys)  := y
| []           ys      := 0
| (x1::x2::xs) ys      := g xs ys
| (x::xs)      (y::ys) := g xs ys + y
| (x::xs)      []      := g xs []

print g._main.equations._eqn_1
print g._main.equations._eqn_2
print g._main.equations._eqn_3
print g._main.equations._eqn_4
print g._main.equations._eqn_5
print g._main.equations._eqn_6