replaced apply-style proof for instance Multiset :: plus_ac0 by recommended Isar proof style
Lomega = Base +
rules
pi_bb "[| A:[]; !!x. x:A ==> B(x):[] |] ==> Prod(A,B):[]"
lam_bb "[| A:[]; !!x. x:A ==> f(x):B(x); !!x. x:A ==> B(x):[] |]
==> Abs(A,f) : Prod(A,B)"
end