set.props.boolean(property)

Makes a compare object with a property function that has the following logic:

A(true) ∪ B(false) = undefined

A(undefined) \ B(true) = false
A(undefined) \ B(false) = true

It understands that true and false are complementary sets that combined to undefined. Another way to think of this is that if you load {complete: false} and {complete: true} you've loaded {}.