# -(_:_:) Subtracts one amount from another. ``` static func - (lhs: BTCAmount, rhs: BTCAmount) -> BTCAmount ``` ## Parameters `lhs` The amount to subtract from. `rhs` The amount to subtract. ## Return Value The difference, in satoshis. May be negative. ## Discussion> Precondition: The difference fits in `Int64`; traps on overflow.