Many types of toilet seat arrangements require a way of retaining the seat and cover in the vertically upright position.  One example of such an arrangement is a toilet seat fabricated from thick foam.  In this case, when the seat is raised and resting against the toilet seat cover, which in turn is resting against the toilet tank, the thickness of the seat results in the latter forming an angle less than or equal to ninety degrees with the horizontal so that it remains in an unbalanced state, whereby it may readily drop down to the horizontal position. 
Various prior art devices are known for retaining toilet seats and toilet covers in the upright position.  Generally, these devices include a bracket which fits over the top edge of the toilet tank and a rigid retaining member pivotally connected to the bracket which swings into engagement with the seat and cover thereby holding same against the toilet tank in the upright position. 
A drawback to these types of devices are that they take up a lot of room, which makes them inconvenient to use, particularly when the toilet is in cramped quarters.  Also, by being rigid, they have a fixed length and therefore being non-adjustable may not be useable, if for example, a thicker toilet seat was used to replace a thinner seat.