Still the most outstanding problem currently left unresolved in mathematics must be Doormat's Penultimate Theorem. Just before he died, in a tragic chip-butty related accident, Conjugate Doormat jotted down an incomplete outline of his now-infamous theorem on the ample left breast of the Miss July centrefold in the issue of Playboy he was perusing at the time. He meant to go back to the theorem at a later date and transfer it to his working journals. But, only five days later, Doormat was found dead, a still-warm chip-butty in his hand and his penultimate theorem left unresolved.
In this, his penultimate theorem, Doormat claimed that he had - at least theoretically - resolved one of the greatest quandaries in applied mathematics. A quandary that has puzzled applied mathematicians and physicists for several hundred years: namely, just how long do you have to dunk a biscuit in a cup of tea to obtain a perfectly-dunked biscuit?
Too short a time and the biscuit absorbs too little tea and is still hard. But, dunk even slightly too long and disaster strikes as the over-dunked portion of biscuit is irretrievably lost in the depths of the tea cup.
One of the major difficulties of this problem has been to find a universal law of biscuits that will apply across the range of all biscuits, from, for example, Rich Tea right through to the thickest of shortbread fingers. It is possible to create a rule for a virtual biscuit under strict laboratory tea-dunking conditions, but this is of little practical use outside of the laboratory.
It is this real world applicability that Doormat claimed for his theorem that makes the quest to resolve it so intriguing for applied mathematicians. If a mathematician could just work out the - of necessity - complex maths that would turn biscuit-dunking from an art into an exact science the rewards from a grateful world freed forever from the heart-rending trauma of over-dunked biscuit loss could be immense.