types

PPD :: S: Stock
       P: Pricelist
       E: EquipDb;

Stock = map Unit to Quantity;

Unit = Equip | Comp;

Quantity = nat;

Equip :: K: nat;

Comp  :: K: nat;

Pricelist = map Comp to Currency;

Currency = real;

EquipDb = map Equip to map Unit to Quantity