  A reconstruction problem is formulated for multisets over commutative
groupoids. The cards of a multiset are obtained by replacing a pair of its
elements by their sum. Necessary and sufficient conditions for the
reconstructibility of multisets are determined. These results find an
application in a different kind of reconstruction problem for functions of
several arguments and identification minors: classes of linear or affine
functions over nonassociative semirings are shown to be weakly reconstructible.
Moreover, affine functions of sufficiently large arity over finite fields are
reconstructible.
