Conway's base 13 function is a function created by British mathematician John H. Conway as a counterexample to the converse of the intermediate value theorem. In other words, it is a function that satisfies a particular intermediate-value property — on any interval ( a , b ) {\displaystyle (a,b)} , the function f {\displaystyle f} takes every value between f ( a ) {\displaystyle f(a)} and f ( b ) {\displaystyle f(b)} — but is not continuous.