Minimum quantity for "(p/b) impossible optical illusions" is 1.
Minimum quantity for "(p/b) the ultimate book of optical illusions" is 1.
Minimum quantity for "(p/b) action optical illusions" is 1.
Minimum quantity for "(p/b) topsy-turvy optical illusions" is 1.
Minimum quantity for "(p/b) ambiguous optical illusions" is 1.