Wednesday, March 1, 2017, 2:00 pm

Many problems can be expressed in the following form, or are closely related to such one: given a set H in a group, what is the maximal size of a set A such that A-A is inside H, or is disjoint to H. Examples: sets on the plane without unit distance; mutually orthogonal bases; Littlewood's problem on simultaneous approximation of two numbers.